chore(dev): update agent skills

[alexey-igrychev]

Summary

Agent guidance committed with trdl now uses the current workflow, review, test-verification, and session-retro procedures, adapted to this repository. This changes how agents prepare and assess trdl changes; it does not change trdl runtime behavior.

What

• Agents creating branches, commits, and pull requests follow current workflow conventions; branch/base rules name main and release-please release-v* branches, not another project's version branches.
• Agents reviewing a diff use the current review skill; the obsolete rigorous-review skill is removed.
• The review skill checks against trdl facts: multi-module layout (server/, client/, release/, e2e/), the Linux-only CGO Vault plugin, GPG/TUF security paths, task server:*/client:*/release:*/e2e:* build and test commands, TRDL_* (and TRDL_VAULT_*) env counterparts, task docs:gen for reference pages, release-please ownership of CHANGELOG.md, samber/lo server-only usage, and AI-test naming (*_ai_test.go, //go:build ai_tests, TestAI_).
• Agents changing tests follow the current test-falsifiability procedure; agents receiving review feedback apply its updated response guidance.
• Agents can run the current session-retro procedure after work completes.
• No instruction references or assumes another project's tools, config, release branches, or dependencies.
• trdl binaries, CLI behavior, Task targets, and release artifacts do not change.

Why

The committed copies had diverged from the current shared skill procedures, and the imported text carried assumptions specific to another project (release branches, deploy engine, container backends, giterminism). Left as-is, agents would receive guidance that is wrong for trdl. Adapting the procedures to trdl's own layout, security model, and task commands keeps the skills useful here without a project-specific fork of unrelated rules.

[alexey-igrychev]

Verification

• Confirmed .agents/skills contains no werf reference and no leftover foreign-project terms (nelm, helm, buildah, buildx, giterminism, stapel, kubedog, netavark, WERF_).
• Cross-review by an independent reviewer agent informed the trdl adaptation of the review skill; findings were folded back into this branch.
• Ran git diff --check.

Review focus

• .agents/skills/review/SKILL.md — verify the trdl gotchas (Vault/TUF security paths, Linux-only CGO server plugin, multi-module coordination) and task/TRDL_* claims match the repository.