fix(memory): align session file counter denominator with indexer filter

The scanSessionFiles function in extensions/memory-core/src/cli.runtime.ts counts session transcript files using entry.name.endsWith(".jsonl"), but the session indexer at src/infra/session-cost-usage.ts:386 uses isUsageCountedSessionTranscriptFileName() which excludes non-session .jsonl files (trajectory artifacts, compaction checkpoints, archive backups).

This mismatch inflates the totalFiles count shown in the memory status CLI output, confusing operators who compare it against the actual indexed session count.

What changed

• Import isUsageCountedSessionTranscriptFileName from the existing plugin SDK export at memory-core-host-engine-qmd
• Replace .endsWith(".jsonl") with isUsageCountedSessionTranscriptFileName(entry.name) in the scanSessionFiles filter

The function is already used by the indexer at src/infra/session-cost-usage.ts:386 — this change aligns the counter with the same filter.

Real behavior proof

• Behavior addressed: Session file counter in memory status CLI used a broader filter than the session indexer, causing inflated totalFiles counts.
• Environment tested: macOS, Node.js, openclaw local build from upstream/main
• Steps run after the patch:
  1. Verified the import resolves: node -e to call isUsageCountedSessionTranscriptFileName with test filenames
  2. Verified filter correctness: primary session transcripts return true, trajectory/checkpoint/archive files return false
  3. Ran node scripts/run-vitest.mjs run extensions/memory-core/src/ — 63 test files, 934 tests passed
  4. Ran pnpm build — built successfully in 79.6s
• Evidence after fix:

node -e "const{isUsageCountedSessionTranscriptFileName}=require('./dist/plugin-sdk/memory-core-host-engine-qmd.js'); const tests=[['session-abc123.jsonl',true],['my-session.trajectory.jsonl',false],['session-abc.jsonl.reset.1718000000',false],['session-abc.jsonl.deleted.1718000000',false],['session-abc.jsonl.bak.1718000000',false],['sessions.json',false],['my-session.checkpoint.a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d.jsonl',false]]; let p=0; for(const[n,e]of tests){const g=isUsageCountedSessionTranscriptFileName(n); if(g!==e)console.log('FAIL:',n,'expected',e,'got',g); else p++;} console.log(p+'/'+tests.length+' passed');"
7/7 passed

grep -n "isUsageCountedSessionTranscriptFileName" extensions/memory-core/src/cli.runtime.ts
12:import { isUsageCountedSessionTranscriptFileName } from "openclaw/plugin-sdk/memory-core-host-engine-qmd";
530:      (entry) => entry.isFile() && isUsageCountedSessionTranscriptFileName(entry.name),

• Observed result after fix: Counter now uses the same filter as the indexer. Non-session .jsonl files (trajectory, checkpoints, archives) are excluded from the count.
• What was not tested: Live memory status CLI output comparison (requires running OpenClaw with actual session files). The function behavior is verified via direct invocation and existing test suite.