MSRV 1.86→1.96, collapsible_if→let_chains, unwrap audit, WAL size, do…

[parv68]

…c sync

P1: Bump MSRV from 1.86 to 1.96

• Replace all 49 #[allow(clippy::collapsible_if)] with let_chains syntax
• Update rust-toolchain.toml, CI matrix, README badges

P2: Production unwrap() audit

• Fix 7 of 8 fixable unwraps (postgres conn, mysql rows, rbac relation)
• 36 SAFE unwraps documented, 1 QUESTIONABLE investigated

P3: wal_size_mb() for rocksdb

• Scan .log files in DB directory for WAL size estimate

P4: connection_stats() + wal_size_mb() for mysql

• Pool status from mysql_async, innodb_log_file_size query

P6: Documentation sync

• IMPLEMENTATION.md test count 280→327
• aegis-test-plan.md: ci.yml not test.yml
• Remove stale CHANGELOG/ROADMAP files

Other: README rewrite (~650 lines), memory audit chain,
condition.rs unwrap fix, dead code removal, org URL cleanup