feat(symphony): tracker-agnostic orchestrator plugin

Sketch of a Claude Code port of openai/symphony — a daemon-style
orchestrator that polls an issue tracker, dispatches isolated worker
agents per issue, and reconciles state across ticks. Tracker-agnostic
by design: the project's CLAUDE.md documents how to talk to whatever
tracker is in use (GitHub Issues, Gitea, tracker CLI, Linear, etc.);
the plugin reads those instructions rather than shipping per-tracker
adapters.

Includes:
- /symphony-init for first-time setup (detects gh/gitea/tracker, writes
  the tracker section into project CLAUDE.md, drops WORKFLOW.md, offers
  to schedule the tick)
- /symphony-tick fired by /schedule cron entries (idempotent, silent,
  never prompts)
- per-issue worker agent in isolated worktrees
- on-disk state in .symphony/state.json (survives cron cold starts)

Known divergences from the spec are documented in the plugin CLAUDE.md
(no streaming agent telemetry; no codex.* knobs; hooks run inside the
worker rather than the orchestrator).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

symphony/templates/state.schema.json

@@ -0,0 +1,44 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Symphony orchestrator state",
+  "type": "object",
+  "required": ["running", "retry_attempts", "claimed", "completed"],
+  "properties": {
+    "running": {
+      "type": "object",
+      "additionalProperties": {
+        "type": "object",
+        "required": ["task_id", "worktree", "started_at"],
+        "properties": {
+          "task_id": { "type": "string" },
+          "worktree": { "type": "string" },
+          "started_at": { "type": "string", "format": "date-time" },
+          "issue_identifier": { "type": "string" }
+        }
+      }
+    },
+    "retry_attempts": {
+      "type": "object",
+      "additionalProperties": {
+        "type": "object",
+        "required": ["attempt", "due_at_ms"],
+        "properties": {
+          "attempt": { "type": "integer", "minimum": 1 },
+          "due_at_ms": { "type": "integer" },
+          "last_error": { "type": ["string", "null"] }
+        }
+      }
+    },
+    "claimed":   { "type": "array", "items": { "type": "string" } },
+    "completed": { "type": "array", "items": { "type": "string" } },
+    "totals": {
+      "type": "object",
+      "properties": {
+        "ticks":       { "type": "integer" },
+        "dispatched":  { "type": "integer" },
+        "completed":   { "type": "integer" },
+        "failed":      { "type": "integer" }
+      }
+    }
+  }
+}