Implement ADR-0021: PE pipeline refactor with token self-routing

Step 1-2: Backup existing code
- builtin/ → builtin_legacy/ (unchanged backup)
- custom/pe_accel/ → custom/pe_accel_legacy/ (unchanged backup)

Step 3-4: New pipeline types and tiling
- pe_types.py: StageType, Stage, TilePlan, PipelinePlan, PipelineContext, TileToken
- tiling.py: generate_gemm_plan, generate_math_plan (ported from pe_accel)

Step 5: Component implementations (ADR-0021 D4-D6)
- PE_SCHEDULER: _feed_loop (singleton FIFO feeder) + plan generation
- PE_FETCH_STORE: new component — TCM ↔ Register File
- PE_GEMM: TileToken pipeline + legacy PeInternalTxn dual-mode
- PE_MATH: TileToken pipeline + legacy dual-mode
- PE_DMA: TileToken pipeline + legacy + fabric Transaction triple-mode
- PE_TCM: TcmRequest handler with dual-channel BW serialization

Step 6: Infrastructure
- topology.yaml: pe_fetch_store component + chaining edges
- components.yaml: pe_fetch_store_v1 registration
- builder.py: PE_COMP_OFFSETS, _add_pe_internal_edges, PE view positions
- Tests: node/edge counts, PE component sets updated

All components handle both TileToken (pipeline) and PeInternalTxn (legacy).
Token self-routing: components read next stage from token.plan, chain via out_port.
366 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_topology_compile.py

@@ -19,16 +19,16 @@ def test_full_graph_node_count():
     # + 2 SIPs x (1 IO x 23 io_nodes
     #            + 16 cubes x (32 routers + 1 hbm_ctrl + 1 m_cpu + 1 sram
     #                          + 20 ucie (4 ports x (1 port + 4 conn))
-    #                          + 8 PEs x 7 pe_comps))
+    #                          + 8 PEs x 8 pe_comps))  (ADR-0021: +pe_fetch_store)
     #   IO: pcie_ep + io_cpu + noc + 4 io_ucie_ports + 4*4 io_ucie_conn = 23
-    #   cube: 32 + 3 + 20 + 56 = 111
-    # = 1 + 2*(23 + 16*111) = 1 + 2*(23+1776) = 1 + 3598 = 3599
-    assert len(g.nodes) == 3599
+    #   cube: 32 + 3 + 20 + 64 = 119
+    # = 1 + 2*(23 + 16*119) = 1 + 2*(23+1904) = 1 + 3854 = 3855
+    assert len(g.nodes) == 3855
 
 
 def test_full_graph_edge_count():
     g = _graph()
-    assert len(g.edges) == 10874
+    assert len(g.edges) == 12922  # ADR-0021: +pe_fetch_store + chaining edges
 
 
 # -- Full graph: specific nodes exist -----------------------------------------
@@ -286,7 +286,8 @@ def test_cube_view_pe_to_router():
 def test_pe_view_has_all_components():
     v = _graph().pe_view
     assert set(v.nodes.keys()) == {
-        "pe_cpu", "pe_scheduler", "pe_dma", "pe_gemm", "pe_math", "pe_mmu", "pe_tcm"
+        "pe_cpu", "pe_scheduler", "pe_dma", "pe_fetch_store",
+        "pe_gemm", "pe_math", "pe_mmu", "pe_tcm",
     }