chore(deps): update chacha20 to 0.10.2 and drop the yank exception

[henry40408]

chacha20 0.10.0 and 0.10.1 are both yanked upstream — a yank, not a security
advisory (the only RUSTSEC entry for the crate, RUSTSEC-2019-0029, is against
0.1.x). 0.10.2 was published 2026-08-27 and has now cleared the 7-day hold on
fresh releases, so this takes it and removes the stop-gap advisories.ignore
entry that #161 added to deny.toml.

The crate is transitive only, via rand 0.10.2 under sqlx-postgres and
axum-test:

chacha20 v0.10.2
├── rand v0.10.2
│   ├── rust-multipart-rfc7578_2 v0.9.0 → axum-test v21.1.0 [dev-dependencies]
│   └── sqlx-postgres v0.9.0 → sqlx v0.9.0
└── rand v0.10.2 → sqlx-postgres v0.9.0 → sqlx-macros-core → sqlx-macros

The e2e/ workspace keeps its own lockfile and pinned the same yanked version,
so it is bumped too. CI only runs cargo deny check at the repository root, so
that lock was not failing anything — there is just no reason to leave a second
lockfile on a yanked release.

Lockfiles and config only; no source change, hence no test — nothing about the
program's behaviour changes. README screenshots are unaffected (no template,
CSS or rendered copy in the diff).

Verification

cargo deny check (exit 0):

advisories ok, bans ok, licenses ok, sources ok

cargo nextest run (exit 0):

     Summary [  62.914s] 672 tests run: 672 passed, 0 skipped

cd e2e && cargo check --all-targets (exit 0):

    Finished `dev` profile [unoptimized + debuginfo] target(s) in 29.96s

Closes #162

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.31%. Comparing base (6fb2ad7) to head (a2d549c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #165   +/-   ##
=======================================
  Coverage   96.31%   96.31%           
=======================================
  Files          28       28           
  Lines       13132    13132           
=======================================
  Hits        12648    12648           
  Misses        484      484           

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