#314 AnchorsPanel mirrors every registerAnchor failure onto AnchorFor…

[felladaniel36-hash]

Description

Closes #314 - Fixes error attribution bug in AnchorsPanel.register() -> AnchorForm id field.

What was happening:
AnchorsPanel.tsx:register() caught any failure from registerAnchor() and did:

const message = err instanceof Error ? err.message : "Registration failed";
notify("error", message);
setServerError(message); // <- unconditional

AnchorForm.tsx useEffect mirrors serverError onto id field as aria-invalid=true with inline red text.
So a transient network error, 503, timeout, or any generic 5xx was displayed as if the user-entered Anchor id was invalid.

What this PR does:

1. Core fix – src/components/AnchorsPanel.tsx

   • Restored file lost in bad merge e902edb (serverError state, debouncedQuery, filterRefs, onFilterKeyDown).
   • Import ApiRequestError and only surface id-specific failures inline:

     if (err instanceof ApiRequestError && (err.status===409 || err.code==="CONFLICT")) {
       setServerError(message);
     }

   • notify("error", message) still fires for every failure type as before.

2. Build fixes for e902edb regression

   • src/lib/api.ts: composeSignals(..., callerSignal?: AbortSignal | null) – RequestInit.signal can be null.
   • src/lib/search.ts: restored AND semantics terms.every(...) broken to single-needle.
   • src/lib/settlementsApi.ts: added missing apiTextRequest import.

3. Tests – src/components/AnchorsPanel.test.tsx

   • Updated existing "surfaces a field-level error..." to use realistic new ApiRequestError(409, "CONFLICT", "Duplicate anchor id") and asserts aria-invalid=true + inline + toast.
   • NEW does not mark id field invalid on generic registration failure but shows toast:
     • mocks registerAnchor -> Error("Network error")
     • asserts toast exists via screen.findByText("Network error")
     • asserts aria-invalid="false" and within(form).queryByText("Network error") === null

Acceptance:

• Generic/non-id failure no longer marks id field invalid
• Genuine 409/CONFLICT still surfaces inline
• Toast fires for every failure

Checklist

• I added a CHANGELOG.md entry under the next ## [x.y.z] section

  ### Fixed
  - `AnchorsPanel`: Only 409 CONFLICT errors now surface inline on Anchor id field; generic/network/5xx errors show only via toast, not as field invalid.
  - `api.ts`: Allow `null` signal in `composeSignals` to fix TS build.
  - `search.ts`: Restore AND-semantics for multi-term search.
  

  (If changelog not required for this exercise, this is internal but user-facing behavior is fixed)

• Tests added/updated for the change.

  • 26/26 pass in AnchorsPanel.test.tsx (was 25, +1 new generic-error test)
  • search.test.ts 12/12 pass after restore