feat: agent-orchestrator v0.1.0 — generic multi-agent harness

Extracted and generalized from a project-specific agent launch engine. No project
specifics remain in code: paths, the loop kickoff preamble, handoff conventions, and the
on-complete hook are all config/template driven; session_prefix + log_dir are required.

- agents.py: driver + watchdog (data-driven backends via prompt_delivery arg|ping|exec;
  required session_prefix/log_dir; project-rooted path resolution; configurable kickoff
  template, handoff patterns, on_complete task; tmux-safe; selftest + init verbs)
- agent-log.py: config-driven claude transcript renderer
- agents.example.toml: self-contained 2-agent example (dependency-free demo backend)
- prompts/: generic builder/adversary/kickoff templates
- smoke.sh: isolated up+down sandbox proof that cleans up after itself
- flake.nix/.lock: devShell (python311 + tmux + git)
- README.md: schema + verbs + AI-PO usage + nix

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/PLAN-demo1.md

@@ -0,0 +1,8 @@
+# Example phase: demo1
+
+A placeholder phase plan for the example project. In a real project this file is the single
+source of truth for the phase: its mission and its Definition of Done. The Builder reads it,
+builds, and claims each gate; the Adversary verifies from a cold start and records PASS/FAIL.
+
+## Definition of Done
+- (example) the thing builds and the Adversary records a fresh PASS.

examples/PLAN-demo2.md

@@ -0,0 +1,7 @@
+# Example phase: demo2
+
+A second placeholder phase, to show phase auto-advance and a per-phase model override
+(see `models = { builder = "claude-opus-4-8" }` in agents.example.toml).
+
+## Definition of Done
+- (example) the second deliverable is Adversary-verified.