edition: user-facing errors and docs point to a commercial edition users cannot obtain #68

Observation on main faf1d88 (1.9.8)

Several user-facing surfaces direct users to a commercial edition that is not available from this repository or from npm:

• src/pptx/edition.ts — the hard-deny message for master writes reads Master slide editing requires the commercial edition (edition=community). Theme, master, layout and advanced-chart writes are all hard-denied through editionGatedWriteKind.
• README.md:19 describes the private deckuse-commercial overlay; README.md:397 says "Master/layout editing is available in the commercial edition repository". The seven translated READMEs carry the same text.
• docs/edition.md is written entirely around the community/commercial split.
• pnpm check:no-commercial-leak (scripts/assert-no-commercial-leak.mjs, test/cli/commercial-leak-guard.test.ts, .github/workflows/ci.yml:23, scripts/release.sh:76) guards a boundary that only matters while an overlay is being published.

Impact

An agent or user who hits UNSUPPORTED_CAPABILITY on a master/layout/theme write is told to use a product they have no way to get. The practical outcome is that the agent edits source/ XML directly or switches tools, which bypasses the workspace transaction and history guarantees.

Decision needed

For each of the four gated write kinds (theme, master, layout, advanced chart), pick one:

1. Implement the write in this tree and remove the gate, or
2. Keep it rejected, but report it as a plain "not implemented yet" capability with no edition wording.

Acceptance

• No error message, README, or doc tells users to obtain another edition unless a public way to obtain it is linked.
• docs/edition.md and the README edition paragraph match the decision above.
• The leak-guard script, test, CI step and release step are either kept with a stated purpose or removed together.
• test/pptx/edition-gates.test.ts is updated to the new behavior.