Evaluate the navigation diagrams as permanent documentation

Six diagrams of the book/segment/verse/phrase/token navigation surface were produced while reviewing #235. This issue is to decide which, if any, become permanent docs. If any, where/how should they live in the docs?

The navigation surface spans several independent axes:

• structure,
• coordinate spaces,
• entry points,
• per-scenario causality,
• concurrent state,
• frame-level timing.

No single diagram covers it, so each of the six takes one axis.

The gain: onboarding and change-safety: much of this behavior currently exists only as reasoning inside long doc comments.
The cost: staleness, since each diagram cites specific functions and constants and nothing will flag them when those move. Also, 4 of the diagrams are SVGs, which aren't diffable when updated.

Developed from branch perf/continuous-view-responsiveness @ 0ab3de6 (the open continuous-view perf PR, unmerged). They describe that branch, not main: src/hooks/usePhraseWindowHalf.ts, the holdCentered loop, and the deferred mid-glide re-centre are all branch-only.

Authored by Claude Opus 5 (1M context) — model claude-opus-5[1m] — read from the source on that branch. Every claim traces to a file listed in the README, but none of it has been independently verified by a human.

Temporarily housed at docs/navigation-diagrams, commit 7ab4df0, branched off main.

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The six, to accept or reject individually

1. 01-structure-bands.svg — To-scale band diagram of one stretch of LUK, marking the four places where verse, segment, token, phrase and window boundaries fail to line up.
2. 02-coordinate-spaces.svg — The eight addresses one text position has, and which of the sixteen conversions between them are lossy, partial, or one-to-many.
3. 03-entry-point-matrix.md — Sixteen ways navigation can start, against what each subsystem does about each, plus the asymmetries the empty cells expose.
4. 04-scenarios.md — Six mermaid sequence diagrams: external nav, cross-book jump, arrow step, list click, boundary edit mid-glide, and mode toggle.
5. 05-concurrent-clocks.svg — Harel statechart of the five state machines that run simultaneously, and the six couplings that are the only channels between them.
6. 06-timing-waterfall.svg — Two navigations plotted against frames and the real constants, showing why the settle is event-driven rather than timed.

Start by comparing the six artifacts under docs/navigation with main and the cited branch commit 0ab3de6, then read src/hooks/usePhraseWindowHalf.ts and the README references. Done means each diagram has an explicit accept-or-reject decision, a documented permanent location if accepted, and human verification of claims that currently describe branch-only behavior.