docs: add per-method de-identification quickstart

[abdouloued]

Closes #282.

What

Adds a "Quickstart: choosing a method" section to docs/anonymization.md with a runnable example for each deidentify() method (mask, remove, replace, hash, shift_dates), plus a reidentify() round-trip example. Links to it from docs/getting-started.md.

Every example output was verified by actually running it against the real default model (OpenMed-PII-SuperClinical-Small-44M-v1), not just read from source or checked against mocked unit tests.

Note on #204

The issue asked for a callout documenting the reidentify round-trip limitation tied to #204. That limitation looks already fixed (test_roundtrip_two_persons_mask, commit eb10454, "Closes #222 (addresses #204)"). I documented it as resolved with a forward link to #204/#222 instead of as a current limitation — already discussed with @maziyarpanahi on the issue.

Bonus find

While verifying the shift_dates example against the real model, I found it silently falls back to masking instead of shifting dates for the default English model (entity label stays lowercase date, but the redaction code only matches uppercase DATE). Filed separately as #408 and linked from the doc rather than showing a fabricated shifted-date output.

Verification

• mkdocs build --strict passes.
• Every printed snippet output in this PR is copy-pasted from an actual python -c run against the default model, not hand-written.
• Full test suite green aside from pre-existing, unrelated failures (confirmed identical via git stash).

[maziyarpanahi]

Thank you @abdouloued. I reviewed this against #282 and the issue discussion, then added a maintainer follow-up commit: docs: tighten deidentification quickstart examples.

What changed:

• linked the README privacy section directly to the new anonymization quickstart, satisfying the remaining issue scope;
• updated the remove example to show repr() so the documented trailing space is explicit;
• replaced the placeholder replace output with the deterministic seeded output from the runtime check: asnyder@example.com.

Verification:

• /Users/maziyar/Developer/openmed/.venv/bin/python snippet check for mask, remove, replace, hash, shift_dates, and reidentify() -> matched the documented outputs
• uv run mkdocs build --strict --site-dir /tmp/openmed-pr409-site -> passed
• /Users/maziyar/Developer/openmed/.venv/bin/pre-commit run --files docs/anonymization.md docs/getting-started.md README.md -> passed

I copied #282 labels onto the PR. The branch is mergeable with no conflicts. GitHub has not reported hosted checks for this fork head, so the validation above is local.