Render timeline blocks in widgets

[edwin-zvs]

Summary

• Add a widget Markdown timeline container extension
• Render top-level bullet/checklist items as a connected vertical list, without a nested timeline border/title
• Support timeline item states: done, active/current, blocked/warning, todo, and bullet fallback
• Expose supported widget Markdown extensions through agentd_context so agents can discover the syntax

Syntax

:::timeline
[x] Inspect auth flow
[~] Patch local-only guard
[ ] Run checks
[!] Blocked: missing env
Plain milestone
:::

Also accepted:

:::agentd-timeline
...
:::

Validation

• cargo check -p agentd-cli
• cargo test -p agentd-cli ui_panel_replay_tracks_create_patch_delete
• cargo build -p agentd-cli
• cargo check -p agentd-cli -p agentd-protocol -p agentd-adapter-zarvis
• cargo test -p agentd-protocol agent_context
• cargo build -p agentd-cli -p agentd-adapter-zarvis
• git diff --check