feat: memory debug logs

[mattrossman]

• Adds dev-only heap probes around startup, AppMessage, layer setup, and forecast redraws.
• Logs forecast payload size plus redraw low-watermark samples for allocator churn debugging.
• Compiles the logging out of release builds and documents the helper in AGENTS.md.

Related: #119

[Copilot]

Pull request overview

This PR adds dev-only heap observability to help debug Aplite memory pressure (Issue #119) by instrumenting heap snapshots and low-watermark sampling around startup, AppMessage handling, layer lifecycle, and forecast redraws.

Changes:

• Add a memory_log.h helper with dev-only macros for heap snapshots and scoped low-watermark probes.
• Sprinkle heap probes across watchface init/teardown, window/layer create/destroy, AppMessage receive/open, and forecast redraw/refresh.
• Enable the feature in dev builds via a build flag set from the generated package profile, and document usage in AGENTS.md.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
wscript	Reads build profile and injects FCW2_ENABLE_MEMORY_LOGGING CFLAG for dev builds.
src/c/appendix/memory_log.h	Introduces MEMORY_LOG_HEAP and heap probe macros (dev-only).
src/c/watchface.c	Adds heap snapshots around boot/init and teardown.
src/c/windows/main_window.c	Adds heap snapshots after load and around unload.
src/c/appendix/app_message.c	Logs forecast payload size and heap after app_message_open().
src/c/appendix/config.c	Logs heap after config load/refresh.
src/c/layers/forecast_layer.c	Adds redraw low-watermark sampling and refresh-size heap logging.
src/c/layers/weather_status_layer.c	Adds heap snapshots around update/create/refresh/destroy.
src/c/layers/time_layer.c	Adds heap snapshots after create and around destroy.
src/c/layers/loading_layer.c	Adds heap snapshots after create and around destroy.
src/c/layers/calendar_layer.c	Adds heap snapshots after create and around destroy.
src/c/layers/calendar_status_layer.c	Adds heap snapshots after create and around destroy.
src/c/layers/battery_layer.c	Adds heap snapshots after create and around destroy.
AGENTS.md	Documents how to use the heap probe macros.

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