docs: two POC modes — branch vs standalone scratch project

- pocs.md: define both modes + per-POC assignment (POC-1/2 standalone at
  /workspace/alkgit-pocN, POC-3 branch mode); findings are the
  deliverable, POC source never merges to main
- sdd_process.md: phase 0 + POC Specialist sections cover both modes
- poc-specialist.md: mode determination up front, standalone environment
  section, 'stay in your lane' principle updated
- AGENTS.md: lifecycle status describes the two modes

Verified: none needed (markdown only)

docs/research/pocs.md

@@ -1,8 +1,24 @@
 # alkgit POC Plan
 
-POCs live in research worktrees (`.worktrees/research/<task-id>/`) per
-sdd_process phase 0, or as scratch experiments outside the main workspace
-tree if a worktree isn't available yet. Each POC records: hypothesis,
+## POC modes
+
+POCs are not production code — fewer constraints (comments, unwrap, error
+taxonomy are all relaxed), and their code never merges to main. Two modes,
+chosen by whether the POC touches code in this repo:
+
+- **Branch mode** (POC depends on alkgit code in the repo): create a git
+  branch off main, do the work there, then **merge the findings into the
+  research docs** on main and drop the branch — the POC code itself does
+  not merge.
+- **Standalone mode** (POC is independent of alkgit code): a scratch crate
+  or project at `/workspace/<poc-name>` (e.g. `/workspace/alkgit-poc1`),
+  outside the repo entirely. Findings are written directly into
+  `docs/research/` on main.
+
+In both modes the deliverable on main is the findings write-up, not the
+POC source. POC source is disposable once findings are recorded.
+
+Each POC records: hypothesis,
 method, result (proceed/pivot/block), and what it changes in the research
 docs.
 
@@ -68,4 +84,13 @@ for receive-pack sizing.
 
 POC-1 first (the BiStream/packetline fit is the load-bearing assumption).
 POC-2 next (the crux of fetch). POC-3 last (http shape). Each POC updates
-the corresponding research doc with results and a proceed/pivot/block note.
+the corresponding research doc with results and a proceed/pivot/block note.
+
+## Modes applied to these POCs
+
+- POC-1, POC-2: **standalone mode** — nothing in the alkgit repo exists to
+  build on yet; run as `/workspace/alkgit-poc1` and `/workspace/alkgit-poc2`.
+  (If POC-1's bridge turns out to want the workspace deps, it can flip to
+  branch mode on the repo instead — decide before writing, not after.)
+- POC-3: **branch mode** — it exercises alkhttp wiring against this repo's
+  skeleton; findings merge into `alk-stack.md`, branch is dropped after.