[P2][Decision] Align packaging promises with checkout-dependent runtime paths

[realmarcin]

Problem

CommunityMech currently presents two incompatible runtime models.

pyproject.toml defines a build backend and communitymech console script, implying that a wheel installation is supported. However:

• package data declares only py.typed; schemas and Jinja templates are not explicitly shipped;
• communitymech.paths derives a repository root from __file__ and expects kb, docs, caches, and reports beside the source checkout;
• multiple commands read or write repository-owned artifacts by default;
• paths.py already acknowledges that a wheel install resolves these locations incorrectly.

Priority

P2: this needs a human product and distribution decision. It should not block the immediate P0 safety fixes or P1 documentation corrections.

Decision options

A. Checkout-dependent repository application

• State explicitly that CommunityMech commands run from an editable source checkout.
• Avoid promising standalone wheel behavior.
• Keep repository-relative defaults, but validate checkout presence and fail clearly.

B. Installable package and configurable data application

• Ship schemas, templates, and other runtime package resources.
• Resolve package resources with importlib.resources.
• Make KB, cache, report, docs, and output roots configurable.
• Define safe defaults for installed console-script use.

A hybrid is acceptable only if its boundary is explicit and tested.

Acceptance criteria

• Record the chosen support model and rationale in an in-repository architecture decision.
• Define which CLI commands must work from a wheel and which require a checkout.
• Audit schemas, templates, and other runtime resources against that decision.
• Create scoped follow-up implementation issues for path handling, package data, and installation tests.
• Update README and CLAUDE.md through [P1] Rebuild README quick start and examples from executable repository behavior #665 and [P1] Rewrite CLAUDE.md as a current operational guide for agents #666 to reflect the decision.
• Do not silently write into site-packages or an ephemeral virtual environment under any supported mode.