docs: add progressive-disclosure agent guidance

[zguesmi]

Independent of #346 / #347 / #348. Based on main, docs only, no code touched.

CLAUDE.md is the entry point an agent reads on every task, so it holds only what applies to every task, plus a table pointing at five topic files under .claude/context/:

File	Read when
conventions.md	creating or editing any file, committing, opening a PR
architecture.md	changing contracts, storage, facets, deployment, chain config, orders, registries
commands.md	running a command beyond package.json#scripts, reasoning about CI and generated files
testing.md	writing or debugging tests, using the test helpers
upgrades.md	scripting or executing a facet upgrade

The point of the split is cost: the entry point stays small enough to load every time, and the detail is pulled in only when the work touches it.

One file was missing

CLAUDE.md pointed at .claude/context/conventions.md, which did not exist — a dangling reference. It is written here, and collects the invariants that matter and are not derivable from the code: the SPDX header pair, the published surface in package.json#files (so ABI and artifact changes are public API changes), the append-only storage rule, the generated files that must never be hand-edited, the two hand-maintained facet lists in utils/proxy-tools.ts and scripts/tools/sol-to-uml.mjs, and the squash-merge / Conventional Commits rules.

Also

.claude/worktrees is added to .gitignore. Now that .claude/ is tracked, an agent worktree created inside the repository would otherwise show up as untracked files.

Follow-up if #348 lands

.claude/context/architecture.md names IexecInterfaceToken.sol and IexecEscrowTokenFacet, which is correct against main today. #348 retires both names, so whichever of the two merges second needs a one-line touch-up.

Verification

npm run format:check — All matched files use Prettier code style. No contract, test or script file is touched, so the build, storage, doc, typecheck and test gates are unaffected by this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.54%. Comparing base (26772eb) to head (fc94391).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #349   +/-   ##
=======================================
  Coverage   99.54%   99.54%           
=======================================
  Files          32       32           
  Lines        1095     1095           
  Branches      223      223           
=======================================
  Hits         1090     1090           
  Misses          5        5           

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