fix(agentos): keep chunked_sqlite metadata pieces under the remote SQLite bind limit

[eersnington]

• chunked_sqlite saves its index (the file tree) as one byte array split into pieces, one INSERT per piece.
• Remote actor SQLite rejects a statement whose bound values exceed 128 KiB. With 256 KiB pieces, every save failed once the index grew past 128 KiB.
• Pieces are now 64 KiB. File chunk defaults are unchanged.

// before
const METADATA_CHUNK_SIZE: usize = 256 * 1024;
// after
const METADATA_CHUNK_SIZE: usize = 64 * 1024;

Code: crates/native-sidecar/src/plugins/chunked_sqlite.rs

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This is part 2 of 4 in a stack:

•  4  fix(agentos): route CompareVmConfig through the sidecar request loop #2018
•  3  perf(agentos): batch chunked_sqlite index saves into transactions #2017
•  2  fix(agentos): keep chunked_sqlite metadata pieces under the remote SQLite bind limit #2016 👈
•  1  fix(agentos): accept [ as a package command name #2015

[the-company-company]

🔴 1 high-severity finding

_{Reviewed commit b2215e7.}

[the-company-company]

✅ No issues found

_{Reviewed commit 0d99114.}