Bump to 0.8.0, close Target 12, and record what is still missing

Collision changed the collide slot's signature and grew four public structs, so
this is an ABI break and the soname moves to libakgl.so.0.8. The manual's counts
move with it: 195 functions across 23 headers, 183 of which return an error
context.

Target 12 -- "collision for 256 actors under 2 ms without the caller writing a
broad phase" -- is met. A new benchmark times the whole step with a world
attached, which is the number the target is actually about rather than a
narrowphase call in isolation: 15.4 us at 64 actors, and 54.1 us at 256 in a
purpose-built -DAKGL_MAX_HEAP_ACTOR=256 configuration. Over that 4x range the
step grew 3.5x while the all-pairs control grew 15.6x, which is the n-squared
the index exists to avoid. Plan item 7 is rewritten to record what shipped and
why both partitioners exist; the Construct and Phaser citations stay.

Three new TODO entries. Actor rotation, scoped to the five places it touches and
the one place it does not -- collision_support is written so rotating `dir` in
and the answer back is the whole narrowphase change, and rotational *response*
is explicitly a different piece of work. The swept narrowphase FLAG_BULLET
reserves, with the tunnelling arithmetic written out so a game can check its own
numbers against 1280 px/s. And the ccd arena being single-threaded and sized by
measurement at 7,264 bytes per GJK/EPA box pair.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71

docs/02-design-philosophy.md

@@ -214,7 +214,7 @@ in the tree negated it, which is the only reason that was latent rather than liv
 
 ## Errors carry context, and callers cannot ignore them
 
-**Every one of libakgl's 156 functions returns `akerr_ErrorContext AKERR_NOIGNORE *`.**
+**183 of libakgl's 195 functions return `akerr_ErrorContext AKERR_NOIGNORE *`.**
 Results come back through pointer parameters; the return value is always the error. The
 `AKERR_NOIGNORE` attribute makes discarding it a compiler diagnostic.