Rewrite AGENTS.md with current project structure and file location guide

[sebastientaggart]

Rewrites AGENTS.md from scratch to reflect the current state of the project and help agents orient themselves without searching.

Key changes:

• Fixed branch strategy from development to dev
• Added "Where things live" section organized by purpose (source skills, generated output, adapters, config, docs, build files)
• Added "Skill anatomy" section covering frontmatter, placeholders, conditionals, and change detection
• Added Make targets table
• Expanded working-on-CodeCannon sections (editing skills, adding adapters, adding new skills)
• Updated self-hosting to mention all four adapter outputs
• Strengthened guardrails (commit source+generated together, don't invent placeholders)
• Complete project layout including docs/, .codecannon.yaml, VERSION, ROADMAP.md

Motivation: Agents were observed searching for file locations ("Let me find where the installation documentation is") that AGENTS.md should have told them directly.

Issue #43

[sebastientaggart]

Review Summary

Verdict: APPROVE

Findings

No issues found. Code looks correct and follows project conventions.

Verification notes:

• All file paths and directory structures documented in the new AGENTS.md match the actual repo layout (docs/, docs/skills/, adapters/, templates/, VERSION, ROADMAP.md all exist and are accurately described).
• Branch strategy correctly updated from development to dev (matches INTEGRATION_BRANCH = dev in Makefile).
• Make targets table accurately reflects the actual Makefile targets.
• VERSION example ("0.3.3") matches the current file contents.
• The README.md addition for submodule update instructions uses "Code Cannon" (two words), consistent with the rest of README.md. AGENTS.md uses "CodeCannon" (one word), consistent with its own convention and actual file/directory names.
• No secrets, build artifacts, or .env files included.
• The templates/codecannon.yaml path referenced in the placeholder instructions is correct (file exists at that path).