docs(skills): drop the Mode 2 routing notes, fix the contributing steps

Seven skills carried a `## Mode 2 Routing Note` citing a routing pod ("Plan 6")
that does not exist. Several admitted in their own text that nothing about the
skill changes between modes — so it was roughly ten lines of context on every
load for zero behavioural effect. The content is not worthless, just not
per-skill: it now lives as one table in README.md, with the caveat that nothing
depends on it.

The related line inside the session_log sections stays, because that one does
motivate behaviour — but it no longer cites a component that has never shipped.
It now says what is true: pass-rate is what a future routing decision would be
based on, and a skill that never logs contributes no evidence either way.

While in README: the contributing steps were stale enough to fail CI for anyone
who followed them. They said to add a row to SKILLS_INDEX.md by hand — the table
is generated now, and `task check` fails on a hand-edited diff — and listed none
of the four frontmatter keys the gates require. Step 4 now names the
pressure-test bar from #19 rather than leaving it to be discovered.

Closes #36
Bump-Type: patch

skills/tdd/SKILL.md

@@ -419,7 +419,7 @@ treats `pass` as success, `fail` as failure, `skip` as neither.
 - `fail` — the phase's intended outcome was NOT reached (test compiled when it shouldn't, test still fails after green attempt, refactor broke tests).
 - `skip` — phase was skipped intentionally (e.g. refactor not warranted).
 
-**Why this matters:** the routing pod (Plan 6) reads pass-rate to decide whether to route a future `tdd` call to a local model. If your skill never logs, the routing pod sees no data and may default-route or default-not-route in a way that doesn't reflect real performance.
+**Why this matters:** pass-rate is what a future routing decision would be based on — whether a `tdd` call can be served by a local model instead of a cloud one. A skill that never logs contributes no evidence either way, and a decision made on no evidence is a coin flip wearing a metric.
 
 ## Final Rule
 
@@ -429,7 +429,3 @@ Otherwise → not TDD
 ```
 
 No exceptions without Mathias's permission.
-
-## Mode 2 Routing Note
-
-This skill is invoked identically whether the agent is running in Mode 1 (cloud Claude, no routing) or Mode 2 (client-local, supervisor routing layer). The routing pod (Plan 6) does not exist yet; until it does, treat this skill as Mode 1 only. The discipline does not change between modes — only the model behind the call.