docs(migrate): add the migrate glossary and the forced-pass obligation ADR

[tobyhede]

Summary

@cipherstash/migrate moves an existing database column between plaintext and encrypted form, tracking each step in a cs_migrations table so an interrupted move can resume. The review of #1193 (the reverse, decrypt direction) kept reopening one question: may an interrupted --force backfill continue without --force? The answer was being worked out separately in each command. This PR writes down the shared vocabulary and the decision agreed for the follow-up design in #1217, so that future PRs argue from the same terms.

Changes

• Glossary: languages/typescript/packages/migrate/CONTEXT.md defines column migration, direction, source and target column, twin, phase, dual-writing, abort, rollout, backfill pass, run, forced pass, obligation and waiver. Each entry lists the words to avoid.
• ADR: languages/typescript/packages/migrate/docs/adr/0001-forced-pass-is-an-obligation.md. A forced pass is an obligation recorded on the column migration, and @cipherstash/migrate enforces it for every caller. While the obligation is open, every run is forced. Only a completed forced pass or, in the up-front reverse case, a recorded waiver closes it. At most one column migration is open per column pair.
• Context map: CONTEXT-MAP.md lists the new Migrate context.

Verification

Documentation only. The new files are outside the package's files list, so nothing reaches the npm tarball and no changeset is needed.

Related

Refs #1217, #1193

Review notes

Some terms (reverse direction, waiver) describe behaviour that arrives with #1193 and #1217, so this is best merged after #1193.

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