chore(packages): remove unused packages/ workspace stubs

[Harry19081]

Problem

packages/ has never been wired into the build. pnpm-workspace.yaml
declares packages: ["."], so none of its three packages were installed
workspace members, and a repo-wide search finds zero imports of
@orgii/ui, @orgii/marketplace, or @orgii/orgii-core — the only
occurrence of any of those names is in the packages' own package.json
files.

The cost is not just dead weight:

• @orgii/ui was being maintained despite being unreachable. It held
  a duplicate of the chat font scale. The live implementation is
  src/styles/_chat-typography.scss (which defines .chat-text,
  .chat-text-xs, .chat-code-sm) plus the --chat-font-size write in
  src/app/root/useAppShellEffects.ts:152. Commit 0cf7cbbb
  ("style(chat): tighten chat pane font size scale") edited both
  copies in lockstep — so every font-scale change was paying a tax on a
  file that does not participate in the build, and a future divergence
  between the two copies would have been invisible.
• @orgii/marketplace and @orgii/orgii-core were empty skeletons
  (.gitkeep files only) for an OSS/commercial package split that was
  never built. packages/README.md described that plan as in progress
  and pointed at docs/rust-backend/oss-boundary--0506.md, which does
  not exist in this repository. Anyone following that README would have
  been working from a plan the repo had already abandoned.

Solution

Delete packages/ in full, along with every reference that only existed
to serve it:

• scripts/ci/detect-rust-changes.cjs — drop the packages/ prefix from
  FRONTEND_ONLY_PREFIXES. Beyond pointing at a directory that no longer
  exists, the deleted skeletons contained packages/*/src-tauri/ paths,
  so had that layout ever been filled in, this entry would have silently
  skipped Rust CI for Rust changes. Removing it fails safe: a future
  packages/ would now trigger Rust CI unnecessarily rather than skip it
  wrongly.
• scripts/ci/detect-rust-changes.test.cjs — drop the corresponding
  packages/ui/src/styles.scss fixture line.
• .github/dependabot.yml — drop the "not covered here, deliberately"
  note about packages/*.
• docs/contributing/wiki/Architecture-Overview.md — the AGPL-3.0
  rationale row pointed at packages/orgii_core as a planned OSS core.
  Reworded to state the licensing rationale without the dangling
  reference. Prettier reflowed that table's column widths as a
  consequence of the longer cell; no other row changed in content.

No src/ or src-tauri/ file is touched.

Potential risks

Low, and the failure mode would be a build error rather than silent
breakage.

• Nothing imported the deleted code. Verified by searching the full
  tree (excluding node_modules, .git, target) for @orgii/ui,
  @orgii/marketplace, @orgii/orgii-core, ChatFontStyles,
  packages/ui, and packages/orgii — after this change there are zero
  hits.
• The chat font behavior is unchanged. The CSS classes and the
  --chat-font-size variable are defined and consumed entirely within
  src/; the deleted copy was never loaded.
• CI Rust-skip behavior changes only for a path that does not exist.
  With packages/ gone, no diff can start with that prefix today. The
  change matters only if the directory returns, and then in the
  conservative direction.
• Recreating packages/ later is unaffected. It was never a
  workspace member, so a future package (for example a shared market
  client) starts from the same position it would have started from
  before this PR: pnpm-workspace.yaml needs packages/* added.

Verification

Commands run in a clean worktree off develop:

• node --test scripts/ci/detect-rust-changes.test.cjs — 6/6 pass
  (the suite that covers the edited allowlist).
• npx tsc --noEmit -p tsconfig.json — clean, no diagnostics. Note this
  is weak evidence on its own: packages/ was never in tsconfig.json's
  include set, which is part of why the code was dead. The conclusive
  check is the reference sweep below.
• Reference sweep for @orgii/ui, @orgii/marketplace,
  @orgii/orgii-core, ChatFontStyles, packages/ui, packages/orgii
  across the tree — zero hits post-change.
• Pre-commit hook (lint-staged, prettier, eslint/circular stats) ran and
  passed on the commit.

Not run: full vitest and cargo test. No TypeScript or Rust source
under src/ or src-tauri/ is modified, and the pre-commit hook
reported "No TypeScript files staged, skipping type check" and "No Rust
files staged, skipping clippy" for the same reason. The one behavior this
PR does change — the CI Rust-skip allowlist — is covered by the
node --test run above.