feat: yield the terminal and browser to DSH 0.1.6's own sidebar types

DSH 0.1.6-alpha.2 ships a right-Sidebar terminal and a right-Sidebar browser
of its own. Both were things this plugin had built from scratch, so keeping
them meant two implementations of one surface plus a plugin that shadows a
host type the product is actively developing.

Terminal: the plugin's whole PTY stack goes — the UI-tab manager, the
agent-owned registry, the lazy node-pty loader, the eight model-facing
terminal_* tools, the xterm view and its font/link/scrollback helpers, and
the cross-session 'pinned terminal' rail that existed only to keep a terminal
alive across a session switch. The host's terminal kind becomes the only
provider, which also retires the node-pty dependency, its pnpm allowBuilds
entry, and the installer's -Repair mode (issue #140's whole class of
'node-pty failed to load' support).

Model-facing capability note: the plugin used to inject terminal_* tools
(off by default). Those are the model's only cross-call persistent terminal,
and DSH's own equivalent (@deepseek-ai/dsh-tool-terminal) is not mounted by
any shipped bundle, so removing them leaves the model with the one-shot
bash/pwsh tools only. That is the accepted cost of not maintaining a second
PTY surface; the README documents how to enable the upstream toolset.

Browser: the plugin's browser tab type is dropped, so the host's own browser
kind owns embedded pages. The DOM-level link takeover STAYS (it is the only
thing that can route an https link to the system browser by protocol, which
the host does not do) but now delegates to the host's browser tab via
ctx.sidebarRight.openTab('browser', …) with a window.open fallback, and the
two settings that only ever configured the plugin's own iframe (sandbox
escape hatch, loopback allowlist) go with it — along with the host-side
browser.probe route they fed.

Cards: the empty-pane welcome cards adopt the host's guide-capsule recipe
(0.5px l4 hairline, 24px radius, layer-1 fill, 56px floor, 14px/20px padding)
so the plugin's 'pick what opens here' surface reads as the same design as
DSH's own. A theme.spec guard pins the geometry and the token-only paint —
including that the upstream-only --dsw-alias-bg-l1/-l2 spellings (defined
nowhere, so their declarations are silently dropped upstream) never appear
here.

Also drops the dead state the removed features left behind (SidebarTab.pin,
nextTerminal, agentWaits, bottomOpenedOnce, the agent-tab helpers, the
pinned-tab memo key), re-points every test fixture that used them at
surviving equivalents, and prunes the specs of the deleted features.

src/client/api.ts

@@ -10,7 +10,6 @@ import { encodeHtmlUrl } from '../html-route.ts'
 import type { LastActivity } from '../subagent-activity.ts'
 import type { SidechatLiveEvent, SidechatLogEvent, SidechatThreadInfo } from '../sidechat-core.ts'
 import type { SidebarSessionEvent } from '../context-types.ts'
-import type { BrowserProbeResult } from './browser.ts'
 
 /** One wire failure. */
 export class SidebarApiError extends Error {
@@ -114,21 +113,6 @@ export interface JobOutputResult {
 /** The `subagents.live` response: running child id → latest activity. */
 export type SubagentLiveResult = { live: Record<string, LastActivity> }
 
-/** Terminal dependency status (mirror of the host's depsStatus; issue #140). */
-export type TerminalDepsStatus =
-  | { ok: true }
-  | {
-    ok: false
-    /** The require-time error message (module missing, native binding broken…). */
-    cause: string
-    /** The pasteable repair command (terminal/cmd). */
-    command: string
-    /** The detected profile name (null when undetected → the command defaults to web). */
-    profile: string | null
-    /** Optional supplementary hint (fallback command only). */
-    note?: string
-  }
-
 /**
  * Parse one `/sidebar` JSON response envelope into its value. A non-ok
  * status, an unparseable body, or any shape other than `{ok: true, value}`
@@ -338,23 +322,6 @@ export const api = {
   /** Cherry-pick one commit onto the current branch. */
   gitCherryPick: (scope: SessionScope, hash: string, worktree?: string) =>
     call<{ ok: true }>('git.cherry-pick', gitPayload(scope, worktree, { hash })),
-  /** Release a terminal's process immediately (tab closed; the WS close frame
-   *  may be unreachable while the socket is down, so the host also accepts
-   *  this explicit route). */
-  ptyClose: (scope: SessionScope, tab: string) =>
-    call<{ ok: true }>('pty.close', scopePayload(scope, { tab })),
-  /** Release an agent terminal by uuid (tab closed while WS was down). */
-  agentPtyClose: (uuid: string) =>
-    call<{ ok: true }>('agent-pty.close', { uuid }),
-  /** Skip every active terminal_wait_for on one agent terminal (the wait
-   *  banner's skip button). Idempotent: {skipped:0} when none is active. */
-  agentSkipWait: (uuid: string) =>
-    call<{ ok: true; skipped: number }>('agent-pty.skip-wait', { uuid }),
-  /** Terminal dependency status (issue #140): after a WS close 1011 with
-   *  reason `pty-deps-missing` the view fetches the full repair details here
-   *  (the close reason itself is capped at 123 bytes). */
-  terminalDeps: () =>
-    call<TerminalDepsStatus>('terminal.deps', {}),
   /**
    * The output the model has read so far for one background job (replayed
    * from the owner session's event log — never the model's job_output
@@ -403,9 +370,6 @@ export const api = {
       childId,
       ...(afterSeq !== undefined ? { afterSeq } : {}),
     }, signal),
-  /** The effective terminal shell and its display name (plugin-global). */
-  shellGet: () =>
-    call<{ shell: string; name: string }>('shell.get', {}),
   /** Read the side card preferences (plugin-global, no session scope). */
   settingsGet: () =>
     call<{ value?: unknown; revision?: number; externalDisable?: boolean }>('settings.get', {}),
@@ -415,10 +379,6 @@ export const api = {
       patch,
       ...(expectedRevision !== undefined ? { expectedRevision } : {}),
     }),
-  /** Probe a URL's response headers (the sidebar browser's embeddability
-   *  check; see the host's browser.probe route). */
-  browserProbe: (url: string, signal?: AbortSignal) =>
-    call<BrowserProbeResult>('browser.probe', { url }, signal),
   /** External open for the file tree's "open with" menu. Remote SSH editor
    *  URLs are launched on the browser/client machine; reveal and local URLs
    *  keep using the host's platform opener. */