structure: backends into src/{tty,gui,lsp}, pane kinds and builtins into their own files

The core now lies FLAT at src/ and every subdirectory is one backend, so a
file being in no directory at all is what says it is core. Pane-kind bodies
leave pardes.zig for term_pane.zig / file_pane.zig / output_pane.zig, leaving
it the layout, the event/effect machine and the generic render loop.

Builtins are one struct each in builtins.zig, and the enum is folded out of
the file's own declaration list at comptime — a zig file IS a struct, so the
list of builtins and the builtins themselves are the same text. Adding one is
writing a struct. Key paths deliberately stay one table for the config pass.

Pure refactor: no golden moved.

1 files changed, 2 insertions, 2 deletions

diff --git a/docs/lsp-evaluation.md b/docs/lsp-evaluation.md
index 5f660640..1756ec94 100644
--- a/docs/lsp-evaluation.md
+++ b/docs/lsp-evaluation.md
@@ -1,6 +1,6 @@
 # Three language backends, measured
 
-Same core, same seam (`src/lsp.zig`), same 17-probe harness (`zig build lspbench`)
+Same core, same seam (`src/lsp/lsp.zig`), same 17-probe harness (`zig build lspbench`)
 over the same corpus. Three jj workspaces, three independent implementations,
 one function each. C landed; see **Decision** below.
 
@@ -84,7 +84,7 @@ real binary through the helix keymap, and pass `hxdiff` (360) and `hxparity`
 
 ## Decision
 
-**C landed.** It is what `src/lsp_zls.zig` is, and ZLS is now a fetched
+**C landed.** It is what `src/lsp/lsp_zls.zig` is, and ZLS is now a fetched
 dependency (`build.zig.zon`, pinned to commit `3e0d0820` on the 0.16.x branch)
 so it sits in `zig-pkg/` like everything else and the build is reproducible
 from the .zon alone — no path dependency on a local checkout.