docs(js-sdk): document onUploadInit callback for upload resume

[dobby-coder]

Summary

Documents the onUploadInit callback added in encryption4all/postguard-js#71 (merged at dcdd6591) on UploadOptions and CreateEnvelopeOptions. Replaces the stale "Current limitation" paragraph in docs/sdk/js-encryption.md that pointed at encryption4all/postguard-js#68; that issue is now resolved.

The new subsection under "Resume an interrupted upload" covers:

• Signature: (info: { uuid: string; recoveryToken: string }) => void
• When it fires: once, synchronously, after upload_init resolves and before the first chunk PUT
• Use: persist {uuid, recoveryToken} so a later resumeUpload can rehydrate after a process restart
• Caveat from the source JSDoc: runs inside the upload stream's start handler; a throw errors the stream
• Examples for both Sealed.upload and createEnvelope
• Source links pinned to the postguard-js merge commit

Source verified against src/types.ts#L107-L112 (UploadOptions) and src/types.ts#L246-L250 (CreateEnvelopeOptions) at dcdd6591f58976364f8220f4cedbe86d0e2bce3b.

Closes #94

Test plan

• npm run docs:build succeeds (~6s)
• Built dist/sdk/js-encryption.html contains the new onUploadInit content
• Source-link URLs return HTTP 200 at the pinned commit
• Writing style: no banned words, no em dashes, no inflated bold

Reviewer quickstart

git fetch origin && git checkout docs/onuploadinit-callback && npm install && npm run docs:dev

Then open http://localhost:5173/sdk/js-encryption.html#capture-recoverytoken-via-onuploadinit

[dobby-coder]

Reviewed and verified (bot cannot self-approve, so this is a comment review):

• Source links resolve and the line ranges match the JSDoc at dcdd6591 (verified via raw.githubusercontent).
• UploadOptions.onUploadInit is at src/types.ts#L107-L112; the CreateEnvelopeOptions forward is at src/types.ts#L246-L250. Both check out.
• Examples for Sealed.upload and createEnvelope mirror the public API correctly.
• The replaced "Current limitation" paragraph referenced the now-resolved postguard-js#68 follow-up; removal is appropriate.
• npm run docs:build succeeds in ~6s; built page contains the new section.
• Writing style holds: no banned words, no em dashes, no extraneous bold.

No blockers. LGTM, ready for @rubenhensen to merge.

[dobby-coder]

Rule compliance pass found two issues in the PR body (docs content itself is clean):

• Bare cross-repo reference postguard-js#68 — GitHub doesn't auto-link bare repo#NN across repos. Rewrote as encryption4all/postguard-js#68 per the cross-repo-link-format rule.
• Em dash in the same sentence — postguard-docs writing rules target zero em dashes. Replaced with a semicolon.

No code changes.

[dobby-coder]

Verified at commit 0111f3a (bot cannot self-approve, so this is a comment review with an approve verdict):

• Source links return HTTP 200 at dcdd6591; both line ranges match the JSDoc and signatures (UploadOptions L107-L112, CreateEnvelopeOptions L246-L250).
• npm install + npm run docs:build succeed in ~23s; built dist/sdk/js-encryption.html contains the new onUploadInit section.
• Examples for both Sealed.upload and createEnvelope mirror the public API as defined in postguard-js types.
• Replacing the old 'Current limitation' paragraph is correct now that the linked postguard-js follow-up is resolved.
• Writing style is clean: no banned words, no em dashes, no inflated bold.

Verdict: approve. Ready for @rubenhensen to merge.