fix(web): harden clipboard copy and terminal paste flows

[gaius-codius]

Summary

This PR improves copy/paste behavior across desktop + mobile contexts and clarifies copy intent in file view.

Why

• clipboard APIs fail in common environments (permissions, insecure context, mobile webview constraints)
• terminal paste needed a clear fallback path when direct clipboard reads are unavailable
• file view needed clearer distinction between "copy path" and "copy file content"

Scope

Clipboard reliability

• upgrade safeCopyToClipboard:
  • try modern navigator.clipboard.writeText
  • fallback to legacy document.execCommand('copy') strategy
  • preserve selection/focus where possible
  • throw explicit failure only after both paths fail

Terminal paste UX

• add explicit Paste action in terminal quick input area
• when clipboard read works, inject text directly
• if clipboard read fails, open manual paste dialog
• guard against empty clipboard values (no fallback dialog spam)
• keep terminal focus and modifier reset behavior consistent

File view copy clarity

• keep path copy action in file header row
• move file-content copy action into file content block
• only enable file-content copy for safe cases:
  • successful file read
  • non-binary content
  • non-empty content
  • size <= 1,000,000 bytes

i18n

• add terminal paste labels/strings in en and zh-CN

Files touched

• web/src/lib/clipboard.ts
• web/src/routes/sessions/terminal.tsx
• web/src/routes/sessions/file.tsx
• web/src/lib/locales/en.ts
• web/src/lib/locales/zh-CN.ts

Validation

• bun run typecheck
• bun run test:web

Test coverage added in this PR

• Added web/src/lib/clipboard.test.ts
• Added web/src/routes/sessions/terminal.test.tsx
• Covers:
  • clipboard writeText success path
  • execCommand fallback when writeText fails
  • explicit error when both copy strategies fail
  • terminal paste behavior for empty clipboard value
  • terminal fallback modal when clipboard read throws

Validation run (successful)

• bun run typecheck:web
• bun run test:web

Both commands executed after test additions and passed.

[gaius-codius]

Hi Team, I understand you prefer to open an issue first before adding features but these are changes I’ve worked on for my own setup and thought I would share.
This is a fantastic project and has helped me and my workflow immensely.
I have tried to keep the PRs narrow, open to any and all suggestions and comments.

[github-actions]

Findings

• None.

Summary

• No issues found in diff. Residual risk: file-content copy gating tests not found in repo.

Testing

• Not run (automation)

HAPI Bot