ui: brand palette, rendered markdown, and a vertical session nav

[hbrooks]

Summary

• Adds src/lib/theme.ts, the Ellipsis dark palette, as the one source of color for the CLI. Every hardcoded cyan/green/red now reads from it.
• Bone, not brand blue, carries "you are here" in dark mode. Brand ink scores 1.79:1 on the panel, so selection is a brightness step between surfaces.
• Drops inverse video everywhere. Selected transcript lines, sandbox phases, and the composer lighten to a tinted surface instead of flashing white.
• Renders agent markdown as styled ANSI via src/lib/markdown.ts. Bold, headings, bullets, tables, and fenced code stop showing raw asterisks and pipes.
• Pre-wraps rendered text to the pane width, so viewport row estimates are exact instead of guesses and ink has nothing left to re-wrap.
• Caches rendered output per (width, source). The transcript re-renders on every stream frame, so re-parsing history each time would be wasteful.
• Measures ANSI-stripped width for all layout math, because escape sequences occupy no columns.
• Chat messages become full-width tinted panels with a 1-cell pad. The 80%-width assistant column and its metadata gutter are gone.
• Drops per-turn duration and cost summaries from the transcript. The footer's running spend already says it.
• Collapses the settled sandbox block to its headline. → reveals config and sandbox lines, → again opens the phase panel, ← collapses back.
• Turns the session nav from a horizontal windowed bar into a vertical list: + New session plus 5 recent sessions, one row each.
• Moves nav keys to ↑/↓ (was ←/→). esc or ↑ off the top row returns to chat. New navSlice keeps one row of lookahead as the list scrolls.
• Makes the header a tinted band: ellipsis.dev at the left edge, the focused session's id · model · $cost · N tokens at the right, with fallbacks that drop the link, then the model, then the spend.
• Shows @ghLogin in customerLogin when no session is focused, so the header always says who you are.
• Moves the Repository, Agent, and Model rows inside the new-session composer panel. Pickers unfold in place instead of popping up above the input.
• Heads the repository list with the repo detected from the cwd as a normal checkable entry, replacing the Default (detected) row.
• Starts a session idle on an empty prompt via idle_start, so the sandbox spins up and the first composer message opens turn 0.
• Fills the new-session empty state with one random software-lore fact from src/lib/facts.ts, capped at 72 columns.
• Filters laptop sessions out of the nav, and merges polled with composer-spawned sessions by id so a mid-create poll cannot double a row.
• Upgrades to Ink 7, React 19, and SDK 0.4.0, targets node22, drops ink-spinner, and declares chalk and cli-table3 (imported directly, previously only transitive). connect now renders every frame off-TTY so the documented --no-input headless path is not silenced.

Test plan

• npm test: 351 tests pass, including new suites for compactTokens, rowMeta, sessionSource, mergeSidebarSessions, navSlice, withRenderedMarkdown, and facts
• npm run typecheck
• npm run build
• Drive agent interactively: markdown rendering, vertical nav keys, sandbox collapse, idle start from an empty prompt