feat(resume): session resume dropdown with terminal launch and directory actions (wesm#120)

## Summary

Adds a session action dropdown to the breadcrumb bar that lets users
resume sessions in a terminal, open the project directory in editors or
file managers, and copy paths and commands to the clipboard.

### Backend

- **`POST /sessions/{id}/resume`** — Builds the agent-specific resume
command (`claude --resume`, `codex resume`, etc.), optionally launches
it in a detected or user-specified terminal. Supports `command_only` for
clipboard copy, `opener_id` for launching in a specific terminal, and
flags like `skip_permissions` and `fork_session` for Claude.
- **`GET /sessions/{id}/directory`** — Agent-agnostic directory
resolution. Prefers the embedded `cwd` from the session file, falls back
to the session's `project` field. Used by the frontend to determine
dropdown visibility and copy the directory path.
- **`GET /openers`** — Detects installed applications (terminals,
editors, file managers) via app bundle paths on macOS and `PATH` lookup
on Linux. Results are cached with a 60s TTL.
- **`POST /sessions/{id}/open`** — Launches a detected opener with the
session's resolved project directory.
- **Terminal config** (`GET/POST /config/terminal`) — Persisted `auto`,
`custom`, or `clipboard` mode. Custom mode supports a user-specified
binary and argument template with `{cmd}` placeholder.
- **macOS launch** uses `open -na <app>` for `.app` bundles and direct
binary execution for PATH-detected installs, keeping detection and
launch consistent. AppleScript for iTerm2 and Terminal.app.
- **Session directory resolution** reads the first 20 lines of the
session JSONL file for an embedded `cwd` field, with fallback to the
session's `project` field. Both must be absolute paths pointing to
existing directories.

### Frontend

- **Resume dropdown** on the session breadcrumb bar, visible when the
session has resume support, detected openers, or a resolvable directory:
- Terminal openers (Ghostty, kitty, iTerm2, etc.) — launches the resume
command directly
- "Default terminal" — uses the server's auto-detect or custom terminal
config
  - "Copy command" — copies the resume command to clipboard
  - "Copy directory path" — copies the resolved project directory
- "Open in" section — detected editors (VS Code, Cursor, Zed, etc.) and
file managers (Finder, etc.)
- **Keyboard shortcut** `c` copies the resume command to clipboard from
the session detail view.
- **`resume.ts`** utility with per-agent command templates and POSIX
shell quoting.
- **Dropdown visibility** is based on actual capabilities: cached
server-side directory resolution, detected openers, and agent resume
support. No dropdown renders for sessions with nothing actionable.

### Supported agents

| Agent | Resume command |
|-------|---------------|
| Claude | `claude --resume <id>` |
| Codex | `codex resume <id>` |
| Gemini | `gemini --resume <id>` |
| OpenCode | `opencode --session <id>` |
| Amp | `amp --resume <id>` |

### Detected terminals (macOS)

Ghostty, iTerm2, kitty, Alacritty, WezTerm, Terminal.app — detected via
app bundle path with PATH binary fallback for non-default installs.

### Detected terminals (Linux)

Ghostty, kitty, Alacritty, WezTerm, GNOME Terminal, Konsole, Xfce
Terminal, Tilix, xterm — detected via `PATH`. Respects `$TERMINAL`
environment variable.

---------

Co-authored-by: userFRM <frederic.miesegaes@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

frontend/src/lib/api/client.ts

@@ -330,6 +330,34 @@ export function getExportUrl(sessionId: string): string {
   return `${BASE}/sessions/${sessionId}/export`;
 }
 
+/* Resume in terminal */
+
+export interface ResumeRequest {
+  skip_permissions?: boolean;
+  fork_session?: boolean;
+  command_only?: boolean;
+  opener_id?: string;
+}
+
+export interface ResumeResponse {
+  launched: boolean;
+  terminal?: string;
+  command: string;
+  cwd?: string;
+  error?: string;
+}
+
+export function resumeSession(
+  sessionId: string,
+  flags: ResumeRequest = {},
+): Promise<ResumeResponse> {
+  return fetchJSON(`/sessions/${sessionId}/resume`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(flags),
+  });
+}
+
 /* Publish / GitHub config */
 
 export function publishSession(sessionId: string): Promise<PublishResponse> {
@@ -392,6 +420,70 @@ export async function bulkStarSessions(
   }
 }
 
+/* Session directory */
+
+export function getSessionDirectory(
+  sessionId: string,
+): Promise<{ path: string }> {
+  return fetchJSON(`/sessions/${sessionId}/directory`);
+}
+
+/* Openers — Conductor-style "Open in" */
+
+export interface Opener {
+  id: string;
+  name: string;
+  kind: "editor" | "terminal" | "files" | "action";
+  bin: string;
+}
+
+export interface OpenersResponse {
+  openers: Opener[];
+}
+
+export function listOpeners(): Promise<OpenersResponse> {
+  return fetchJSON("/openers");
+}
+
+export interface OpenResponse {
+  launched: boolean;
+  opener: string;
+  path: string;
+}
+
+export function openSession(
+  sessionId: string,
+  openerId: string,
+): Promise<OpenResponse> {
+  return fetchJSON(`/sessions/${sessionId}/open`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ opener_id: openerId }),
+  });
+}
+
+/* Terminal config */
+
+export interface TerminalConfig {
+  mode: "auto" | "custom" | "clipboard";
+  custom_bin?: string;
+  custom_args?: string;
+}
+
+export function getTerminalConfig(): Promise<TerminalConfig> {
+  return fetchJSON("/config/terminal");
+}
+
+export function setTerminalConfig(
+  cfg: TerminalConfig,
+): Promise<TerminalConfig> {
+  return fetchJSON("/config/terminal", {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(cfg),
+  });
+}
+
 /* Analytics */
 
 export interface AnalyticsParams {