fix(workspace): name a workspace by its resolved path

[ningmao-hlyz]

Fixes #1761.

What changed

A folder reached through a symlink became two projects, two conversation
histories and two engines. Both doors where a person's path becomes a key now
resolve symlinks with filepath.EvalSymlinks before keying:

• engineWorkspace (cmd/codeaf/engine.go) — the resolver every engine
  command goes through (--daemon, --status, --stop) and the source of
  the host's workspace name. It stopped at filepath.Clean, so
  sha256(Clean(...)) in enginehost.where minted one host directory per
  spelling: --status <link> missed the engine started at <dir>.
• /project (internal/tui3/projectcmd.go) — the pin stored the raw typed
  spelling, so home keyed the folder under the alias while a launch from the
  resolved path (already canonicalized by v3OpenTarget) keyed it under the
  target: two project rows, one folder.

Regression test: cmd/codeaf/engine_symlink_test.go drives a symlink through
engineWorkspace and asserts both spellings land on the same directory, and
that a plain path still resolves to itself.

Changelog entry: docs/rules/changelog.md names the entry for its pull
request, and the number exists only once the pull request does — so it
arrives in the next push as
docs/changes/unreleased/<this-pr>-symlink-workspace-keys.md
(kind: fixed, surface: [engine, workspace]). The first red on check
is that workflow, not a mistake.

How it was checked

• go build ./cmd/codeaf ./internal/tui3 — exit 0 (go1.26.5).
• go test ./cmd/codeaf -run TestEngineWorkspace -count=1 -v — both tests
  pass: TestEngineWorkspaceResolvesSymlink,
  TestEngineWorkspaceKeepsNonSymlinkPathUnchanged (ok … 2.434s). To run
  this on Windows the other cmd/codeaf test files were moved aside for the
  run and put back — see the limitation below.
• GOOS=linux go vet ./cmd/codeaf ./internal/tui3 — exit 0, the platform CI
  runs, so every test file (including the added one) typechecks there.
• gofmt on the committed blobs — clean (engine.go, projectcmd.go,
  engine_symlink_test.go).
• Reproduction at base 8761488a: a stdlib probe mirroring enginehost.where
  showed sha256(Clean(<link>)) ≠ sha256(Clean(<real>)) — two spellings,
  two host directories — and that EvalSymlinks collapses both spellings to
  one host directory.

Honest limitation: cmd/codeaf's test package does not build on Windows at
all — carried_child_test.go uses fakeFolderProgram, which lives behind
//go:build !windows; the identical failure exists at base 8761488a. So
the full suite cannot run on my Windows checkout and defers to CI on Linux
(where GOOS=linux go vet passes).

Checklist

• A change entry — arrives in the next push, named for this pull request
  (the number does not exist until the pull request does; see
  docs/rules/changelog.md).
• The manual knows about it — no slash command, key, tool, default, limit
  or refusal moved (keying fix only), so internal/manual/chat/ is
  unchanged.
• No new line in .github/known-red.txt.
• Only my own paths are staged — cmd/codeaf/engine.go,
  cmd/codeaf/engine_symlink_test.go, internal/tui3/projectcmd.go.

[CLAassistant]

All committers have signed the CLA.

[santoshkumarradha]

Hey, thanks for the PR. Could you sign the CLA when you get a chance so we can review it?

[ningmao-hlyz]

Hey, thanks for the PR. Could you sign the CLA when you get a chance so we can review it?

done