fix(observability): five React defects incl. Memory Graph crash on fresh installs

[elhoim]

5 commits, one per fix, so each can be cherry-picked independently. Each was verified to apply cleanly onto 47df8ee by itself.

Commit	Fix
bbe709a	stop the Memory Graph route crashing on fresh installs
52552da	clear the Ledger error on a successful poll
d730b30	clear the Algorithm regenerate interval on unmount
9e04106	make Live-sessions rows actually expand
524028c	abort in-flight CapabilityStrip fetches on window switch

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Five React defects under LIFEOS/PULSE/Observability/src/.

• app/memory/graph/page.tsx:257 — data.themes.map crashes the whole Memory Graph route on a fresh install. handleMemoryGraphApi returns a default 200 carrying communities and no themes when the graph file is absent, and the only guard is !data, which a truthy themeless object passes. themes is now optional on the interface and the call site defaults it.
• app/ledger/page.tsx:90 — the success path never cleared error, and if (error) replaces the whole page, so one transient fetch failure pinned the Ledger to its error state permanently.
• app/algorithm/page.tsx:275 — setInterval created inside a click handler rather than an effect, leaking up to 15 minutes of setState on an unmounted component. Adds a ref plus an unmount effect, matching the file's existing idiom.
• components/activity/WorkBoard.tsx:950 — the Live-sessions section hard-coded expanded={false} and a no-op onToggle while BoardRow still rendered the chevron, cursor-pointer and hover background, so the row advertised itself as clickable and did nothing. Wired to expandedId/setExpandedId exactly as the sibling sections are.
• components/activity/CapabilityStrip.tsx:153 — no AbortController or generation guard, so after a window switch the slower 24h response overwrote the newer 1h one.

Verified: tsc --noEmit output is byte-identical to the clean tree (confirmed by stashing and re-running) — the one remaining error is pre-existing in app/telos/_v7/app.tsx, untouched here. next build was deliberately not run: generateBuildId uses a timestamp and distDir is the tracked out/, so it would rewrite committed artifacts, and typescript.ignoreBuildErrors is set so it adds no checking.

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Testing. Commands and output are in the per-file notes above. I did not do a fresh-system install verification (contributing step 3) — these are targeted fixes verified per-file, not an install run.