Add idle-state classifier and Solo-parity timer tools

Classifies every running child as idle/working/thinking/permission/error
using one of three pluggable strategies (output_activity,
osc_title_stability, osc_title_status) plus optional regex promoters
applied to the tail of recent output. State and last-match reason are
exposed via MCP on ProcessInfo and get_process_status. Per-preset
configuration lives on a new preset.IdleDetection block with bundled
defaults for the first-party claude/codex/opencode presets.

OSC title plumbing is exposed as Emulator.Title(), polled from the
session pump after each emulator write so title-change activity feeds
into the classifier without an extra cgo callback.

The MCP timer surface expands to match Solo: timer_set,
timer_fire_when_idle_any/all, timer_cancel, timer_pause, timer_resume,
timer_list. timer_wait is now a thin wrapper that shares the same
manager so it shows up in timer_list while pending. Timer bodies are
delivered to the owner process through the existing
InjectAsOrchestrator path. Top-level (non-agent) callers can attach
timers to a specific process via owner_process_id; omitting it grants
universal cancel/pause/resume/list privileges.

The sidebar gains a state glyph per process row and appends a
nearest-timer indicator when one is pending or paused.

Tests: idle_test.go covers the classify() pure function across the
three strategies and regex promotion; timers_test.go covers the
manager. Harness scenarios cover output_activity, osc_title_stability,
osc_title_status, and regex promotion, plus timer_set delivery,
cancel, pause/resume, idle_any-on-transition, idle_all-pending, and
idle_all-already-satisfied. A new wait_until_mcp harness step type
polls an MCP method until an assertion holds.

internal/app/child.go

@@ -123,6 +123,19 @@ type Child struct {
 	portsMu sync.Mutex
 	ports   []PortSighting
 
+	// Idle-detection state. idleState carries the classifier's current
+	// opinion (StateIdle / StateWorking / …). lastTitleNS is the wall
+	// time of the most recent OSC title change — separate from
+	// lastWriteNS so the osc_title_* strategies can ignore plain output
+	// churn. idleDetection is the compiled per-preset config, resolved
+	// once at spawn and immutable thereafter.
+	idleState     atomic.Pointer[IdleState]
+	idleReason    atomic.Pointer[string]
+	titleMu       sync.RWMutex
+	title         string
+	lastTitleNS   atomic.Int64
+	idleDetection *resolvedIdleDetection
+
 	cleanupMu    sync.Mutex
 	cleanupPaths []string
 	restarting   atomic.Bool
@@ -330,6 +343,75 @@ func (c *Child) IdleMS() int64 {
 	return (time.Now().UnixNano() - last) / int64(time.Millisecond)
 }
 
+// TitleIdleMS returns how many milliseconds since the OSC window title
+// last changed. 0 means "no title set yet".
+func (c *Child) TitleIdleMS() int64 {
+	last := c.lastTitleNS.Load()
+	if last == 0 {
+		return 0
+	}
+	return (time.Now().UnixNano() - last) / int64(time.Millisecond)
+}
+
+// Title returns the most recent OSC 0/2 title.
+func (c *Child) Title() string {
+	c.titleMu.RLock()
+	defer c.titleMu.RUnlock()
+	return c.title
+}
+
+// recordTitle updates the cached title and bumps lastTitleNS when it
+// actually changes. Called from Session.pumpChild after each PTY chunk
+// — cheap because most chunks don't carry an OSC sequence.
+func (c *Child) recordTitle(newTitle string) {
+	c.titleMu.Lock()
+	if c.title == newTitle {
+		c.titleMu.Unlock()
+		return
+	}
+	c.title = newTitle
+	c.titleMu.Unlock()
+	c.lastTitleNS.Store(time.Now().UnixNano())
+}
+
+// IdleState returns the classifier's current opinion. Empty string
+// (StateUnknown) means the classifier hasn't run yet for this child.
+func (c *Child) IdleState() IdleState {
+	p := c.idleState.Load()
+	if p == nil {
+		return StateUnknown
+	}
+	return *p
+}
+
+// IdleReason returns the human-readable reason the classifier last
+// recorded. Empty when no classification has happened yet.
+func (c *Child) IdleReason() string {
+	p := c.idleReason.Load()
+	if p == nil {
+		return ""
+	}
+	return *p
+}
+
+// setIdleState updates idleState + idleReason. Returns true when the
+// state actually changed (so callers can fan out a notification).
+func (c *Child) setIdleState(s IdleState, reason string) bool {
+	prev := c.IdleState()
+	if prev == s {
+		return false
+	}
+	c.idleState.Store(&s)
+	c.idleReason.Store(&reason)
+	return true
+}
+
+// setIdleDetection installs the resolved per-preset idle-detection
+// config. Called once at spawn; not safe to swap at runtime.
+func (c *Child) setIdleDetection(r *resolvedIdleDetection) {
+	c.idleDetection = r
+}
+
 func (c *Child) recordWrite(chunk []byte) {
 	c.lastWriteNS.Store(time.Now().UnixNano())
 	c.screenVersion.Add(1)