fix: keep a d-set favorite from reverting to the init value on restart

wttrin-favorite-location did two jobs: a defcustom the user sets in init, and the savehist-persisted value that `d`/make-default mutated. Setting it in init (setopt) clobbered the `d` choice on every startup. So a favorite promoted with `d` reverted to the init value after a restart, and the mode-line showed the wrong location's weather. wttrin-saved-locations had the same defect.

I split the two roles. The defcustoms stay as the init-set base. New savehist-persisted runtime vars, wttrin--favorite-override and wttrin--saved-locations-runtime, hold what `d`, save, rename, remove, and the geolocation commands write. Reads go through resolvers: wttrin--favorite-location returns the override or the configured favorite, and wttrin--saved-locations overlays the runtime directory on the configured one (runtime wins on a name collision). Init and `d` now write different variables, so neither clobbers the other.

Removing a saved location that only comes from init can't delete it, since the runtime removal has nothing to touch. The command now says so instead of reporting a removal that didn't happen.

There's no automatic migration. A favorite set in init is unaffected, and a favorite set only with `d` before this version is re-set once with `d`. The README documents the behavior.

1 files changed, 2 insertions, 2 deletions

diff --git a/README.org b/README.org
index cd419c1..fd01bf0 100644
--- a/README.org
+++ b/README.org
@@ -108,7 +108,7 @@ Simply use the keybinding you assigned, or run `M-x wttrin` to display the weath
 
 Choose one, or for a quick one-time weather check, type a new location and ⏎ . After the weather is displayed, the footer shows two groups of keys. Keys that act on the view: `a` for another location, `g` to refresh, `q` to quit. Keys that act on your saved locations: `s` to save the shown location, `d` to make it your default, `r` to rename a saved location, and `x` to remove one.
 
-Pressing `d` sets =wttrin-favorite-location= to the location on screen and remembers it across restarts (via savehist), so the mode-line and future sessions follow it. Your default is also offered in the location list the next time you run =M-x wttrin=. Enable =savehist-mode= for the persistence to stick. (On a geolocation-detected buffer, `d` first prompts for a name and saves it — see Naming Locations.)
+Pressing `d` makes the location on screen your default and remembers it across restarts (via savehist), so the mode-line and future sessions follow it. This works alongside a =wttrin-favorite-location= you set in your init: that option is your base default, and a location you promote with `d` overrides it and persists — so a `d` choice is never wiped out by the init value on the next restart. Your default is also offered in the location list the next time you run =M-x wttrin=. Enable =savehist-mode= for the persistence to stick. (On a geolocation-detected buffer, `d` first prompts for a name and saves it — see Naming Locations.)
 
 If you're looking at cached data, a line below the weather art tells you how old it is (e.g., "Last updated: 2:30 PM (5 minutes ago)").
 
@@ -284,7 +284,7 @@ If you don't want to type your city by hand, wttrin can detect it for you.
 
 *From the picker (weather here, right now):* run =M-x wttrin= and pick the first entry, "Current location (detect)". wttrin looks up your city via IP geolocation and shows its weather. If the guess is wrong (VPN, mobile hotspot), the detected city is right there in the buffer header, so just open the picker again and type the correct city.
 
-*Make the detected city your default:* in that weather buffer, press =d=. The detected city becomes =wttrin-favorite-location= (what the mode-line tracks). With =savehist-mode= on, the favorite persists across sessions automatically, since wttrin registers it with savehist. No =customize-save-variable= step is needed.
+*Make the detected city your default:* in that weather buffer, press =d=. The detected city becomes your default (what the mode-line tracks), overriding any =wttrin-favorite-location= you set in your init. With =savehist-mode= on, the choice persists across sessions automatically, since wttrin registers it with savehist. No =customize-save-variable= step is needed.
 
 *Always use my current location:* run =M-x wttrin-use-current-location=, or set the variable directly: