fix(solparq): floor archived-data delete start at lowest archived slot

[picard8472]

Problem

Fixes #61.

--delete-archived-data-range always started its ClickHouse delete at slot 0. Aligned kinds don't archive from the earliest ingested slot: epoch (and custom with --custom-aligned) begin their first archive at an align_up boundary, so the window between the earliest ingested slot and that boundary is never captured by any archive.

With deletion starting at 0, that never-archived window still fell inside [0, safe_end] and got wiped — dropping data that existed in no archive. Example: ingest starts at slot 100 with epoch archiving; the first epoch archive is [432000, 863999], but the delete swept [0, 863999], so 100..431999 was gone from ClickHouse and in no archive. (Original review comment.)

Fix

Floor the delete start at the lowest archived start slot across the configured kinds instead of 0. Any slot at or above it exists in at least one archive and can be safely reclaimed; the never-archived leading window stays in ClickHouse. safe_end (the min of each kind's latest archive end) is unchanged, so the "delete only once every kind has covered it" high-watermark still holds.

For setups that intentionally want the leading, never-archived window purged too, add --delete-archived-data-from-slot-zero (env SOLPARQ_DELETE_ARCHIVED_DATA_FROM_SLOT_ZERO) — server mode only, off by default — which restores sweeping from slot 0.

Changes

• safe_delete_archived_data_range now tracks min(parsed.start_slot) alongside min(parsed.end_slot) and floors the delete start there (clamped to safe_end), unless the new opt-out flag is set.
• New --delete-archived-data-from-slot-zero CLI flag + Config field, gated to --server-mode (errors otherwise). Exposed in the ops JSON.
• Updated crates/superbank-solparq/README.md (Cleanup section, aligned-custom caveat, Options list).

Testing

• cargo test -p superbank-solparq --locked — all pass. Updated the epoch-continuation cleanup test to expect the floored start, and added tests for the from-slot-zero opt-in and the server-mode-only validation.
• cargo clippy -p superbank-solparq --all-targets --locked -- -D warnings and cargo fmt --all -- --check — clean.

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