chore: initialize crate base (manifest, lib stub, licensing, agents)

Phase 0 base for the russh-wrapped SSH adapter (family ADR-003):

- Cargo.toml: single-crate alkssh 0.1.0, MIT OR Apache-2.0, lib only,
  publish exclude list matching the sibling-crate policy; deliberately
  empty [dependencies] — the russh pin is phase 0 research output
  (alknet main's 0.49 is a data point, not the decision). [features]
  carries the fail-closed posture as a comment until the capability
  feature graph lands with the committed architecture
- src/lib.rs: crate-root doc describing the adapter shape and the
  fail-closed feature contract
- LICENSE-MIT / LICENSE-APACHE (alktty's standard texts)
- .gitignore (target/, node_modules/, .worktrees/)
- CHANGELOG.md: Keep a Changelog stub, [Unreleased] initialization
- AGENTS.md: full agent operating instructions — git workflow
  (conventional commits, commit-and-push), 13 project conventions
  (russh owns the wire, fail-closed capability features, key reuse via
  alkvault-backed sources, visible-surface=authorized-surface,
   ALPN as one-way door), verification commands, taskgraph
  task rules, SDD phase 0 lifecycle status, architecture context

Verification: cargo build/test/clippy --all-targets -D warnings and
cargo fmt --check all pass (lib stub, zero deps)

CHANGELOG.md

@@ -0,0 +1,15 @@
+# Changelog
+
+All notable changes to this crate are documented here. The format is
+based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and
+this crate adheres to [Semantic Versioning](https://semver.org/).
+
+## [Unreleased]
+
+### Added
+
+- Initialized: docs-only phase 0 base — SDD process (`docs/sdd_process.md`),
+  opencode agent definitions, rust crate manifest (lib only, no
+  dependencies yet), MIT OR Apache-2.0 licensing. The russh pin, the
+  capability feature graph, and the channel-type mapping table are
+  phase 0 research output (family ADR-003, OQ-08 remaining scope).