savings telemetry is not wired into the search flow (blocks semble#206)

[amondnet]

Finding (surfaced while implementing #75)

csp::stats::save_search_stats exists and is unit-tested, but it is never called from the search flow — no call site in main.rs, mcp.rs, or indexing/index.rs. CspIndex also has no file_sizes field.

Upstream SembleIndex records stats inside search() / find_related():

self._file_sizes = self._compute_file_sizes(root) if root else {}
...
save_search_stats(results, CallType.SEARCH, self._file_sizes, max_snippet_lines)

So today csp savings / ~/.csp/savings.jsonl never receives records from real searches — the savings report has nothing to summarize.

Impact

• csp savings under-reports (no telemetry is written on search/find_related).
• Blocks semble#206 (savings correctness when max_snippet_lines is used): there is nothing to correct until savings is recorded. parity(#198/#206): support max_snippet_lines in MCP/CLI output + savings #75 intentionally left #206 out for this reason.

Proposed work

• Add file_sizes to CspIndex (compute on build from the indexed root).
• Call save_search_stats inside CspIndex::search / find_related (or at the CLI/MCP layer), keyed by the default stats file.
• Then apply semble#206: pass max_snippet_lines into the stats so the "delivered chars" reflect the truncated snippet, not the full chunk.

Refs

• Upstream: fix: Ensure savings are correct when max_snippet_lines is used MinishLab/semble#206 (30d36ad)
• Related: parity(#198/#206): support max_snippet_lines in MCP/CLI output + savings #75 (max_snippet_lines), which this unblocks for #206