docs: the local development loop - #197

README gets a "Local development loop" section covering the three agent inputs
and how to override each: edit the skills tree and just run, build the mcp repo
anywhere and pass --mcp, serve docs from your own supabase/supabase checkout and
pass --content-api. It states where the keys go, and that `compare` is a screen
rather than causal proof.

It also records the one live limitation: `docs seed` needs a docs checkout
carrying supabase/supabase#48364, which is still open. Without it
fetchAllSources unconditionally awaits the lint-warnings source, whose loader
needs the docs GitHub App, and a shared Promise.all turns that into a full
abort before any embedding, so a failed attempt costs nothing. Two upstream
rough edges are named rather than glossed: the seed exits 0 while silently
failing 22 reference pages whose sections exceed the 8192-token embedding
limit, and a local index has no partner-integration pages because that source
reads the hosted misc project.

AGENTS.md is the agent-facing version: which loop to run for a given kind of
change, the spend rules for anything that costs money, and the same
limitations stated as operational guidance. CLAUDE.md points at it.

Verified: smoke 27/27, tsc and biome clean.