fix(terminal): wire Edit menu to active terminal

[htazq]

Root cause

The web MenuBar exposed optional Edit callbacks, but App.tsx never supplied them. The terminal implementations therefore existed only inside each PtyTerminal, so menu clicks closed the menu without reaching the active split/tab. Find Next/Previous also discarded the search bar's current query.

Fix

• Route Edit commands through a tab-id-scoped terminal event so only the active terminal responds.
• Wire Copy, Paste, Select All, Find, Find Next, Find Previous, and Clear Screen.
• Keep unsupported Cut disabled; disable terminal actions for non-terminal tabs and Paste while disconnected.
• Reuse the search bar's actual query/options for Find Next/Previous.
• Cover disabled states, every menu callback, split-view targeting, Find focus/display, and current-query navigation.

Duplicate check

No duplicate issue or PR was found.

Related but distinct:

• Could you add a mouse copy&paste function? #11 covers mouse/context-menu copy and paste and was addressed separately by commit a0d1545.
• 粘贴失败 #48 covers clipboard permission denial preventing later paste.

Verification

• pnpm test — 36 files, 498 tests passed.
• pnpm build — passed.
• pnpm exec tsc --noEmit — passed.
• pnpm i18n:check — passed, 945 keys in both locales.
• Changed source files: eslint --quiet — passed.
• Full pnpm lint remains blocked by the existing unrelated src/components/settings-modal.tsx:308 unnecessary assertion error.

Closes #56