Wire graph→text navigation: cycle node occurrences in the SQL editor

[melonamin]

Closes #23. Builds on the nameSpans / bodySpan fields shipped in #20.

Behavior

• Single click on a node → highlights and scrolls the SQL editor to the node's first nameSpan (falls back to the legacy single span for column nodes, which intentionally don't populate nameSpans yet — gated on IntelliSense: alias.column completion (semantic resolver) [epic] #27).
• Double click on a CTE node → jumps to the bodySpan instead.
• ◀ n/total ▶ badge in the header of selected table/CTE/view nodes — clickable arrows cycle through occurrences. Hidden when the node has fewer than two occurrences (single-occurrence nodes already had their one location highlighted on click; an unclickable "1/1" badge would just be noise).
• Keyboard shortcut: `n` advances, `Shift+n` returns to the previous occurrence. The handler is suppressed inside inputs, textareas, and the CodeMirror editor so it does not eat ordinary keystrokes. Cmd/Ctrl/Alt+n still reach the browser.

Editor coordinate fix

SqlView previously dispatched the analyzer's UTF-8 byte offsets directly to CodeMirror, which expects character offsets. This is a no-op for ASCII SQL but produces incorrect highlights when SQL contains multi-byte characters (e.g., a column comment or table name in CJK / emoji). Now uses `byteOffsetToCharOffset` from `@pondpilot/flowscope-core` for both the active highlight and the issue highlights.

Store changes

• New `focusedOccurrenceIndex` slice plus `cycleOccurrence(direction)` and `focusOccurrence(index)` actions, exposed through `useLineageActions` and `useLineage`.
• Cycling logic lives in the store so it is testable in isolation and shared between the per-node controls and the keyboard shortcut.
• `selectNode` / `selectStatement` / `setResult` reset `focusedOccurrenceIndex` to 0.

Files added

• `packages/react/src/components/OccurrenceCycler.tsx` — the badge component, used in both `TableNode` and `SimpleTableNode`.
• `packages/react/src/hooks/useOccurrenceShortcuts.ts` — global keyboard handler.
• `packages/react/tests/occurrenceCycling.test.ts` — 8 unit tests.

Validation

• `yarn workspaces run typecheck`: clean
• `yarn workspaces run test`: 127/127 passing (including 8 new)
• `just lint-ts`: clean
• `yarn workspace @pondpilot/flowscope-app build`: clean (only the pre-existing chunk-size warning)

What I did NOT verify

I did not run the dev server and click around in a browser — I have no browser access in this environment. The compilation / lint / unit-test surface is green, but please do a quick visual smoke test before merging:

• Click a multi-reference table node → editor scrolls and highlights, badge shows "1/N".
• Click ▶ → highlight advances to next occurrence; wraps after N.
• Press `n` while focus is in the graph pane → cycles forward; `Shift+n` → backward.
• Double-click a CTE node → editor jumps to the parenthesized body.
• Type `n` in the SQL editor → ordinary keystroke, no cycling.

Out of scope

• Edge double-click → JOIN highlight (issue notes it as a stretch; needs edges to carry parsing-context positions, not in this PR).
• Column-level cycling — gated on the alias/scope resolver from IntelliSense: alias.column completion (semantic resolver) [epic] #27.
• Stale-graph banner (UI: stale-graph banner when SQL is edited after analysis #22) — independent issue, but its "disable cycler controls" wiring will be one-line once the banner ships.