Coding-Agent Onboarding

• Added repo-local .agentguard.json support so humans and coding agents can share static SDK defaults without dashboard coupling.
• Added the built-in coding-agent profile with tighter loop and retry defaults for repo automation and coding workflows.
• Added executable starter files under examples/starters/ and aligned agentguard doctor / agentguard quickstart around .agentguard/traces.jsonl.
• Added the docs/guides/coding-agents.md onboarding guide plus doc updates across the README, SDK README, examples, architecture doc, roadmap, and generated PyPI README.

SDK Hardening

• JsonlFileSink now creates parent directories automatically so repo-local trace paths like .agentguard/traces.jsonl work out of the box.
• Repo-config parsing now rejects boolean values in numeric fields to keep local defaults deterministic and auditable.
• init() now still honors repo-level profile defaults when service, budget, or trace path are passed explicitly but guard-profile values are left implicit.
• Invalid AGENTGUARD_BUDGET_USD values now fall back to a valid repo-local budget_usd instead of silently dropping budget enforcement.