ticket: simplify ticket identity fields

.yoi/tickets/20260607-235442-001/resolution.md

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+Completed as part of the coordinated runtime workspace / Pod identity bundle.
+
+Summary:
+- Removed Profile slug/source/registry-derived Pod identity fallback.
+- Kept Profile selection as reusable recipe selection only.
+- Updated startup/spawn paths so runtime Pod identity is supplied explicitly via `--pod` and is not inferred from Profile metadata.
+- Removed the hidden session-specific identity split that preserved old Profile startup behavior.
+
+Merged branch:
+- `runtime-workspace-context` via merge commit `b7a533f`.
+
+Validation and cleanup:
+- Post-merge focused tests, `cargo check -q`, `cargo fmt --check`, `git diff --check`, ticket doctor, and `nix build .#yoi` passed.
+- Runtime-workspace coder/reviewer Pods, worktree, and branch were cleaned up.