fix: preserve capital letters in group names and dismiss stale version banner

[Myasir92]

Summary

Fixes #594

• Bug 1 — Capital letters in group/session names: Removed strings.ToLower() from path generation in CreateGroup, CreateSubgroup, and RenameGroup so that group paths preserve the original casing (e.g., "MyProject" → path "MyProject" instead of "myproject").
• Bug 2 — Stale version update banner: Added InvalidateCache() that deletes the update cache after a successful agent-deck update, and added a periodic re-check (every 5 minutes) in the TUI so the yellow banner auto-dismisses when the binary has been updated externally (e.g., via terminal or brew upgrade).

Files Changed

• internal/session/groups.go — removed strings.ToLower() from 3 path-generation sites
• internal/update/update.go — added InvalidateCache() + called it after successful update
• internal/ui/home.go — added lastUpdateCheck field, periodic re-check tick, and banner dismissal logic
• internal/session/groups_test.go — updated path expectations to match case-preserving behavior
• cmd/agent-deck/group_cmd_test.go — updated path expectations to match case-preserving behavior

Test plan

• Create a group with mixed-case name (e.g., "MyProject") — verify it displays with original casing
• Create a subgroup with capitals — verify same
• Rename a group to include capitals — verify same
• Run go test ./internal/session/... — all group tests pass
• Run go test ./cmd/agent-deck/... — all group reorder tests pass
• Start TUI → trigger version banner → update via terminal → wait ~5 min → verify banner dismisses
• Run go test ./internal/update/... — update tests pass

🤖 Generated with Claude Code

[asheshgoplani]

Reviewed end-to-end. Both bug fixes are correct. Two comments: (1) test suite health, (2) scope packaging.

What I verified

1. Checked out the branch.
2. Ran all group-related tests (TestCreateGroup|Subgroup|RenameGroup|MoveSessionTo|DeleteGroup|Reorder): all PASS.
3. Ran the cmd/agent-deck group tests: PASS.
4. Ran full internal/session: 6 test failures — all are the documented pre-existing SetEnvironment: exit status 1 flake class (memory: agent_deck_tmux_test_env.md, tests: TestSyncSessionIDsFromTmux_* + TestInstance_*). Not caused by this PR — they fail identically on main.
5. Checked for case-sensitivity landmines: no strings.ToLower calls on GroupPath remain in groups.go; other GroupPath == comparisons in the codebase are self-consistent (comparing two groups in the same post-fix world).

Bug 1 — Capitals in group paths (removing strings.ToLower)

Correct fix for the user-visible cosmetic issue. One note:

Backward-compat observation (non-blocking)

Users with existing lowercase paths on disk (pre-fix groups stored as "myproject") will continue to display as lowercase. Newly-created groups get the original casing. That's consistent — no migration needed, no breakage — but users seeing a mix of old-cased and new-cased groups in the same install may find it cosmetically odd. Worth a release-note mention: "Group paths now preserve original casing; existing groups are unaffected."

Bug 2 — Stale version banner

The 5-min re-check + InvalidateCache() after a successful update is the right hook. Would prefer this as a separate PR (see Scope comment below), but the logic itself is fine.

Scope / packaging concern (non-blocking, style feedback)

Two unrelated bugs in one PR is harder to review, bisect, and revert. If either change introduces a regression (say, the update-cache invalidation has a race), reverting Bug 2 also reverts Bug 1 — or vice versa.

Going forward, separate PRs per independent bug class. Would make your fixes easier to land quickly.

For THIS PR, fine to ship together — neither touches overlapping code paths. Just noting for next time.

Test coverage check

• Bug 1: existing group tests updated to expect original casing — good coverage.
• Bug 2: no test added for InvalidateCache() or the periodic re-check. Could be a follow-up regression test: create a session → trigger update banner → call InvalidateCache() → verify cache file gone → simulate tick → verify banner clears.

Approval

LGTM on both behavior changes. They solve real user paper-cuts. Ready to merge when maintainer's happy.