DOCS: Rewrite tutorials around the examples/ controllers (one per example, single-sourced)

[coretl]

Rewrite the tutorials as a single pass once the fastcs.demo example controllers exist, sourcing all tutorial code directly from those living modules. Implements #388 §6.

Decisions (settled with Tom, 2026-07-22)

1. Single source of truth = fastcs.demo. Tutorials literalinclude the finished example modules (consolidated into src/fastcs/demo/, mirroring ophyd-async); CI (tox -e docs) keeps them green so docs can't drift.

2. Four tutorials — a hello-world → complicated-device ladder (five example modules; the old "reusable io= object" rung is gone, because io= objects were replaced by getter/setter callables):

   #	Tutorial	Teaches	Backend	Module(s)
   1	hello world	pure-soft @attr decorator	none	hello_world.py (Example 1 — hello-world: pure-soft @attr decorator device #398)
   2	getter/setter	getter/setter callables in __init__; closes with "for a real family, go declarative →"	temperature	temperature_attr.py (Example 2 — attr getter/setter via __init__ (temperature backend) #404)
   3	declarative	annotated SCPIParam + filler (static metadata) plus composition — sub-controllers/vector + @scan + @command on the full temp controller	temperature	temperature_scpi.py + scpi.py (Example 4 — SCPI device: annotated attributes + per-attribute filler data #405), drawing on controllers.py (Example — composition & methods (temperature controller) #390)
   4	introspectable	bare hints filled from a runtime REST parameter tree	Eiger REST	eiger.py (Example 5 — cut-down Eiger: introspectable controller + REST sim #391)

3. Finished-example walkthrough pedagogy (not the old 15-diff "Code N" build). Retire docs/snippets/static01–15.py and docs/snippets/dynamic.py.

4. One umbrella docs pass, after the examples land (see Blocked by:).

Scope

• Four tutorial pages replacing the current static-drivers / dynamic-drivers split; update tutorials.md nav; keep installation.md.
• All code blocks come from the fastcs.demo modules via literalinclude with region markers (:start-after: / :end-before:). Add the markers to each module as part of writing its tutorial here.
• State the declarative (class-body) / procedural (instance-scope) rule up front, mirroring ophyd-async's declarative-vs-procedural page.
• Teach the post-refactor API only: getter/setter callables and @attr (no io= objects, no AttributeIORef, no DataType, no hand-rolled pydantic filler).
• Framing to reinforce: the io= tutorial is replaced by a recommendation in tut 2 to use declarative for families; tut 3's SCPI is not introspectable (static SCPIParam; SCPIController/SCPIParam in the demo layer, not core); tut 4's backend switch is the lesson.

Key files

docs/tutorials/*, docs/tutorials.md, docs/snippets/* (removed), docs/explanations/, src/fastcs/demo/* (+ its README), docs/conf.py.

Acceptance

uv run --locked tox -e docs green (real CI — docs env doesn't run in the nightly sandbox); every tutorial renders code pulled live from fastcs.demo; no docs/snippets/static*.py remain.

Labels / process

documentation. Deliberately NOT api-convergence — human pedagogy pass, can't verify in the nightly sandbox, depends on the examples; the autonomous nightly job ignores it.

ADR: #388 §6 (0013 declarative/procedural rule)
Parent: #388
Blocked by: #398, #404, #390, #405, #391