Land "Since you were here" from pull #6684's branch, with its duplicate `pull_merged` index taken out #6721

Home now has a "Since you were here" section, built from #6684's branch with its history kept, and the duplicate pull_merged index is gone.

• Index: 20261027090000-home-visit.ts now creates only the home_visit table. I removed its CREATE INDEX IF NOT EXISTS pull_merged_at, which duplicated pull_merged from 20261022120000-flow-indexes.ts.
• Query plan: a new test in test/home-since.test.ts runs EXPLAIN QUERY PLAN on the digest's merged_at range. It asserts the plan uses pull_merged and that pull_merged is the only merged_at index on pull. This is a test, not a by-hand check. The plan query is a simplified version of the real one, without the joins and the visibility = 'public' filter.
• Kept as the reviews accepted it:

- one home_visit row per user, written at most once a minute; - a window of 1 h–7 d, with 24 h on a first visit; - the Since you were here · 2 days heading; - visits recorded only on real navigations; - the same lines on the terminal dashboard, which never moves the window; - the section drawn with listCard and row().

• Timing: the visit-phase test only checks that visit is present in Server-Timing on /; it never times it. I corrected the stale header comment in test/home-since.test.ts that still said "adds no phase over 2 ms".
• Test results: bun test test/home-since.test.ts test/home-200.test.ts passed (10 tests) before the comment fix, and test/home-since.test.ts passed again after it (8 tests). bun scripts/design-lint.ts is clean.
• Not verified: bun x tsc --noEmit failed here with "Cannot find type definition file for 'bun'". I left that for the forge's check.

To try it, open / signed in, load it again after an hour or more, and the heading names the window. The terminal dashboard shows the same lines.

Closes #6711

Home now has a "Since you were here" section, built from #6684's branch with its history kept, and the duplicate pull_merged index is gone.

• Index: 20261027090000-home-visit.ts now creates only the home_visit table. I removed its CREATE INDEX IF NOT EXISTS pull_merged_at, which duplicated pull_merged from 20261022120000-flow-indexes.ts.
• Query plan: a new test in test/home-since.test.ts runs EXPLAIN QUERY PLAN on the digest's merged_at range. It asserts the plan uses pull_merged and that pull_merged is the only merged_at index on pull. This is a test, not a by-hand check. The plan query is a simplified version of the real one, without the joins and the visibility = 'public' filter.
• Kept as the reviews accepted it:

- one home_visit row per user, written at most once a minute; - a window of 1 h–7 d, with 24 h on a first visit; - the Since you were here · 2 days heading; - visits recorded only on real navigations; - the same lines on the terminal dashboard, which never moves the window; - the section drawn with listCard and row().

• Timing: the visit-phase test only checks that visit is present in Server-Timing on /; it never times it. I corrected the stale header comment in test/home-since.test.ts that still said "adds no phase over 2 ms".
• Test results: bun test test/home-since.test.ts test/home-200.test.ts passed (10 tests) before the comment fix, and test/home-since.test.ts passed again after it (8 tests). bun scripts/design-lint.ts is clean.
• Not verified: bun x tsc --noEmit failed here with "Cannot find type definition file for 'bun'". I left that for the forge's check.

To try it, open / signed in, load it again after an hour or more, and the heading names the window. The terminal dashboard shows the same lines.