refactor: drop dev-cycle-profile.yml for conventions + CLAUDE.md facts

The profile was never parsed — it was prose the skill bodies told the model to read, so most slots were dead, constant across every project, or fiction (the whole pipeline block, including the "tdd is opt-in" claim, was enforced by nothing).

Split it in two: constants become fixed conventions named directly by the skills (new docs/conventions.md), and the few genuinely per-project facts move to each project's CLAUDE.md under '## Skills plugin: project facts'. tdd/fieldtest/docwriter are now always available; the only behavioural toggle left is spec auto-sign.

Delete docs/profile-schema.md and templates/project-profile.yml; add docs/conventions.md and a project-facts section to templates/CLAUDE.md.fragment; rewrite all SKILL/agent prose and the pipeline/design/migration/README/INSTALL docs accordingly.

postmortem/SKILL.md

@@ -126,8 +126,8 @@ report.
 Resolve in this order:
 
 1. `--out <path>` if the invoker passed one.
-2. The project profile's `paths.postmortem_dir` (if a
-   `.claude/dev-cycle-profile.yml` exists and defines it).
+2. The project's post-mortem directory, if it has one (its CLAUDE.md
+   project facts).
 3. Default: `docs/postmortems/<session-id-short>-<yyyy-mm-dd>.md`
    under the project root, creating the directory if needed.
 
@@ -199,8 +199,8 @@ If the session is flagged `active`, add one line at the top:
   aggregator. All numbers originate here.
 - **Hand-off target:** the `issue` skill, when a finding is a
   trackable defect worth filing.
-- **Profile slot (optional):** `paths.postmortem_dir` for the
-  report destination.
+- **Report destination (optional):** the project's post-mortem
+  directory, if its CLAUDE.md project facts name one.
 - **Data-source note:** this skill reads only the current
   session's own transcript and subagent logs. It does not crawl
   other projects or other sessions (single-session by design).