feat(ui): reframe Sharing tab to external-client sharing via channels

[dolho]

Implements trinity-enterprise#18 (Access/Sharing redesign epic, trinity-enterprise#16). Frontend-only; no API changes.

The Access tab (#17) already owns Trinity operators — this scopes the Sharing tab to the operator → external-client surface.

Changes

• Google-Docs-style framing — "Share this agent" header; operator language removed (operators are managed on the Access tab).
• Single Restricted ↔ Open control — replaces the two policy checkboxes with one segmented control over require_email/open_access:
  • Restricted → require_email:true, open_access:false (approval-gated)
  • Open → require_email:true, open_access:true (anyone verified)
  • Identity proof stays on for external sharing; a legacy require_email:false agent is shown by its open_access flag and upgraded the next time a mode is picked (documented inline).
• Pending requests kept, reframed as external clients awaiting approval.
• Channels as compact summary rows — new reusable ChannelDisclosure.vue (collapsed by default). Detailed config stays reachable inside the expanded row as a non-regressing interim seam; MCP Execution Query Tools (MCP-007) #19 ("move channel config into dialogs") swaps the body for a modal. No channel functionality removed.
• Distribution nudge — outbound file sharing + public links moved into a separate "Distribution" section (distribution, not client access), per the issue's technical note.

Acceptance criteria

• Sharing tab scoped to external clients + channels only (operator allow-list removed — lives on Access tab)
• External access policy as a single Restricted ↔ Open control
• Pending access requests surfaced here
• Channels as compact summary rows (detailed config deferred to the dialogs issue MCP Execution Query Tools (MCP-007) #19)
• Google-Docs-style "share this agent" framing

Verification

• Both SFCs compile via vue/compiler-sfc (script setup + template).
• npm run check:tokens passes.
• Note: full vite build couldn't run in my sandbox (unrelated stale-node_modules mermaid dep gap in AgentWorkspace.vue, not touched here) — CI installs deps fresh.

Notes

• SharingPanel prop/emit contract (agent-name, shares, @agent-updated) unchanged.
• Channel summary rows use emoji glyphs as a dependency-free placeholder; MCP Execution Query Tools (MCP-007) #19 can swap for brand icons.

🤖 Generated with Claude Code

[github-actions]

⚠️ Nightly unit-suite check skipped — merge conflict against dev.

Resolve by running git merge dev locally and pushing the result. The next nightly run will re-test once the conflict is gone.

[vybe]

Validated: frontend-only Sharing tab reframe (SharingPanel.vue, ChannelDisclosure.vue), implements trinity-enterprise#19. No secrets, checks green. Note: cross-tracker issue — manual status-in-dev bump needed on te#19.