fix: add hickory-dns resolver for musl/Android Termux DNS resolution

[Bahtya]

Summary

• Add hickory-dns feature flag to workspace reqwest dependency, replacing the default DNS resolver with hickory-resolver

Problem

musl's getaddrinfo() hardcodes /etc/resolv.conf lookup, which doesn't exist on Android Termux. This causes all HTTPS requests to timeout with 5-second delays when running the statically-linked musl binary on Android.

Fix

The reqwest hickory-dns feature replaces the system resolver with hickory-resolver, which correctly handles Android's DNS configuration. No code changes needed — the feature flag applies globally to all reqwest::Client instances.

Impact

• Linux (glibc): No change — hickory reads /etc/resolv.conf same as system
• macOS: No change
• Android Termux (musl static): Fixed — bypasses musl getaddrinfo entirely
• Proxy mode: Unaffected — proxy handles DNS, reqwest does not resolve

Closes #163

Test plan

• CI compiles successfully across all targets (x86_64, aarch64, musl)
• Existing integration tests pass
• Manual test on Android Termux: kestrel resolves api.telegram.org without timeout

Bahtya

[Bahtya]

Retroactive Code Review — PR #164

Issue #163 Summary

musl's getaddrinfo() hardcodes /etc/resolv.conf lookup, which doesn't exist on Android Termux, causing all HTTPS requests to 5s timeout. Recommended fix: add reqwest hickory-dns feature flag.

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CRITICAL: Cargo.lock is inconsistent — hickory-resolver packages are missing

The hickory-dns feature was added to Cargo.toml, but Cargo.lock was never regenerated to include hickory-resolver and its dependency tree. Evidence:

1. grep 'name = "hickory' Cargo.lock returns 0 results on the merge commit (15e163e)
2. The reqwest entry in Cargo.lock does not list hickory-resolver as a dependency
3. Per docs.rs/reqwest/0.12.28/features, the hickory-dns feature enables dep:hickory-resolver + dep:once_cell

This means: the committed lock file does not actually activate hickory-dns. If cargo build --locked were used, the resulting binary would NOT use hickory for DNS.

Mitigating factor: CI does NOT use --locked, so cargo auto-updates the lock during builds. The feature would work in CI and release. But the repository state is inconsistent, and adding --locked to CI in the future would break builds.

Action needed: Run cargo update and commit the updated Cargo.lock to include hickory-resolver packages.

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MEDIUM: Unrelated Cargo.lock changes bundled in

The diff shows 247 packages removed, 45 added (+381/-3125 lines), far exceeding what a single feature flag addition should produce. The changes include:

• Removed: All LanceDB/Arrow/Parquet packages (17+ direct, hundreds transitive) — leftover from PR feat(memory): replace LanceDB with tantivy-jieba full-text search #160 where Cargo.lock wasn't regenerated
• Added: tantivy-jieba related packages (cedarwood, jieba-rs, phf_*) — also from PR feat(memory): replace LanceDB with tantivy-jieba full-text search #160

This happened because PR #164's Cargo.lock was regenerated from a state where PR #160's dependency changes hadn't been locked yet, picking up both changes in one shot.

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LOW: native-tls still present despite default-features = false

The reqwest entry in Cargo.lock still includes native-tls, hyper-tls, and tokio-native-tls, even though workspace Cargo.toml specifies default-features = false. Likely another dependency enables reqwest's default features. Not specific to this PR but worth investigating separately.

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POSITIVE: The fix approach is correct

• The feature flag approach is exactly right — reqwest's hickory-dns feature replaces the system resolver globally, no code changes needed
• All 15+ reqwest::Client construction points (telegram.rs, discord.rs, providers/lib.rs, web tools) are covered automatically
• No side effects on Linux/macOS — hickory reads /etc/resolv.conf like the system resolver
• Proxy mode unaffected — proxy handles DNS, reqwest doesn't resolve

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Verdict: Needs follow-up

The Cargo.toml change is correct, but the fix is incomplete without an updated Cargo.lock. A follow-up commit running cargo update is needed to actually pull in hickory-resolver dependencies.