fix: drop incorrect "sdkconfig is git-ignored" claim, document wireguard_lwip divergence

[fudio101]

Two small, unrelated fixes found while auditing zen-clock (a consumer of this component).

components/microlink/Kconfig — credential comment overstated

The Credentials menu asserted as fact that sdkconfig "should be git-ignored" (1 comment line + 3 help texts). That's true for this repo's own examples, but not universally — zen-clock intentionally tracks sdkconfig in git and instead runs a guard script (check_secrets.py) before every commit that fails if a credential Kconfig is non-empty. The old wording put the wrong expectation in front of anyone configuring this component via menuconfig in a project that doesn't gitignore sdkconfig. Reworded to state where the value lives without prescribing how a consuming project must handle version control.

components/wireguard_lwip/README.md — no divergence warning, no upstream-check procedure

Only had the upstream URL. Added:

• A warning that this copy has diverged substantially (own allowed_source_ips[] array vs upstream's single allowed_ip/allowed_mask, plus the ESP-IDF 6.x/GCC 15 patches and WG_DEBUG logging) — future syncs are manual merges, not fast-forwards.
• The one-time git remote add smartalock ... + git log procedure for checking upstream, so it doesn't need to be rediscovered.
• The result of the 2026-08-10 check: three commits past the divergence point (the cryptokey-routing source-IP security fix, a variable rename, two 2022 replay-detection fixes), all already present in this copy.

Verification

Built zen-clock (a real consumer) against this branch — clean build, no Kconfig errors:

RAM:   17.4% (57164 / 327680 bytes)
Flash: 44.9% (1883151 / 4194304 bytes)
========================= [SUCCESS] =========================

🤖 Generated with Claude Code