feat(436): wire validate-wardley-math hook + add owm fence alias

[tractorjuice]

Summary

Closes step 1 of the owner-suggested scope on #436 — the existing validate-wardley-math.mjs hook (271 lines, four checks) was sitting in arckit-claude/hooks/ unregistered. This PR wires it up so Wardley artefacts are validated before the Write tool puts a broken map on disk.

• Refactor hook from Stop-mode disk scan to PreToolUse:Write reading tool_input.{file_path, content}. Removes the 5-minute mtime window and stop_hook_active loop-guard — neither apply on PreToolUse.
• Register in hooks.json under PreToolUse:Write with if: \"Write(/projects/**/wardley-maps/**)\", matching the existing validate-arc-filename / score-validator pattern.
• Recognise the owm fence alias alongside wardley. The wardley-mapping skill examples use ```owm; templates use ```wardley. Both now lint.
• Enforce the unit-square [0, 1] coordinate range on component lines inside the OWM block too — previously only Component Inventory table rows were range-checked.
• hooks/README.md: spell out the hook's event/scope and what it checks.

Blocks via {decision: \"block\", reason} so the model sees the validation report and self-corrects, instead of hitting a hard permission error the user has to read.

Out of scope (follow-ups on #436)

• Dangling references in link / evolve / pipeline, annotation-index reuse, pipeline visibility, and style-name typos — these need a real parser (wardley-script-parser). Captured in the issue.
• Mermaid block validator — sibling issue Add Mermaid syntax validation for generated diagrams (linter / pre-commit hook) #435. The Mermaid wardley-beta bare-digit check already in this hook is the only Mermaid coverage; that's incidental because it's inside the same artefact.

Test plan

• Smoke test 1: dirty input with stage mismatch + out-of-range OWM coord + OWM/inventory mismatch + Mermaid bare-digit token → blocks with all four error classes in the reason field
• Smoke test 2: clean OWM block with matching inventory → empty output (allows write)
• Smoke test 3: Write to a non-wardley path → early exit, empty output
• markdownlint-cli2 on touched README → 0 errors
• Integration test against a /arckit:wardley run in a test repo (recommend arckit-test-project-v48-arckit-as-a-service per the issue) — block path should surface the reason and let the model self-correct on retry

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