feat(instances): enforce active limits, follow cwd sync, and quicktemp lifecycle

[Microck]

• What changed

  • Added instances config support for:
    • follow_cwd_on_attach
    • quick_default_path
    • max_active_sessions
    • max_active_sessions_policy (warn|deny|close_oldest)
  • Added session.EnforceActiveSessionLimit(...) and applied it in both TUI and CLI flows:
    • TUI create/fork/restart
    • CLI launch, session start, session restart, session fork, try
  • Added quick default path fallback in quick/no-path creation paths (TUI + CLI).
  • Completed quicktemp lifecycle:
    • AutoDeleteOnClose persisted in storage/migration data model
    • close/delete semantics updated so temporary sessions clean metadata automatically
    • periodic cleanup path handles already-dead temp sessions.
  • Added discoverability and UX updates:
    • richer close confirmation messaging for temporary sessions
    • help text updated for quicktemp behavior
    • settings panel now includes editable INSTANCE BEHAVIOR controls.

• Why

  • Makes session behavior predictable and configurable across both UI and CLI.
  • Prevents unbounded active-session growth with explicit policy handling.
  • Aligns quicktemp behavior with user expectation (temporary means auto-cleanup).
  • Reduces config friction by surfacing instance controls directly in Settings.

• Behavior notes

  • follow_cwd_on_attach now updates project path from tmux pane path after attach return and during polling.
  • max_active_sessions:
    • warn: proceed + warning
    • deny: block operation
    • close_oldest: kill oldest active session then continue.
  • quick_default_path is used when no group/session context path is available.
  • Temporary sessions (AutoDeleteOnClose) skip undo/recent-session restoration paths when auto-removed.

• Tests

  • Added/updated tests for:
    • instance settings parse/getters
    • active-session limit policies (warn/deny/close_oldest/exclude)
    • CLI warning composition + quick default path resolution
    • quicktemp close/delete behavior and skip-undo semantics
    • confirm dialog and settings panel coverage for new instance behavior controls.
  • Validation run:
    • go test ./... ✅

• Config delta

config_delta:
  affordances:
    - add: "Editable instance behavior controls in Settings panel"
    - add: "Active-session policy enforcement in TUI and CLI flows"
    - add: "Quick default path fallback for no-context session creation"
    - modify: "Temporary session close semantics to auto-delete metadata"
  invariants:
    - add: "When active-session limit is configured, start/create/fork/restart obey configured policy"
    - strengthen: "Quicktemp sessions removed via auto-delete do not populate undo/recent lists"
    - strengthen: "Project path follow uses normalized absolute directory paths only"
  constraints:
    - add: "max_active_sessions <= 0 means unlimited"
    - add: "policy defaults to warn for empty/invalid values"
  rationale:
    - "Unify behavior across TUI and CLI to avoid policy bypass paths"
    - "Expose controls in UI so users do not need manual TOML edits"
  enforcement:
    - conformance: "internal/session/instance_test.go (policy tests)"
    - conformance: "internal/ui/home_test.go and internal/ui/settings_panel_test.go"
    - conformance: "cmd/agent-deck/cli_utils_test.go"