Make the system portable: split config from profile, remove hard-coding

Audit found three things compiled in that shouldn't have been: the User-Agent
carried the author's domain, the cluster threshold and window were module
constants the pipeline never overrode, and the embedding model was pinned --
which blocked the one change most likely to be wanted, swapping in a
multilingual model for native-language sources.

Configuration is now three files with distinct roles: config.toml (machinery),
profile.toml (who the reader is), sources.toml (what to read). All are
relocatable via NEWS_CONFIG_DIR. news/*.py now contains no interest, place name,
feed URL, or personal identifier.

tests/test_config.py keeps it that way: it builds a configuration for an
invented reader and asserts none of the author's identity or preferences reaches
the running code. Writing it immediately found a real bug -- CONFIG_DIR was
resolved at import time, so NEWS_CONFIG_DIR silently did nothing if set after
the module was first imported. Now resolved per instantiation.

Documented the coupling that portability creates: [clustering].threshold and
[scoring].veto_absolute are cosine constants calibrated against one corpus with
one model, so changing [embedding].model invalidates both.

profile/profile.toml

@@ -419,25 +419,13 @@ hn_min_score = 150
 # failure was collecting 32 of them, not collecting shallow ones.
 feedback_actions = ["interested", "not_interested"]
 
-# Embedding stays English-only (bge-small-en-v1.5). Measured 2026-09-08: the
-# same story in Spanish and English scored 0.758 and 0.600 cosine, against a
-# random-pair p99 of 0.634 -- so one of two translation pairs was
-# indistinguishable from an unrelated article. Native-language Italian and
-# Spanish feeds would rank erratically, so Italy and Mexico are covered by
-# English-language sources (ANSA English, Mexico News Daily) instead. Revisit
-# with multilingual-e5-small only if native sources become worth re-calibrating
-# every threshold for.
-embedding_language = "en"
+# Embedding is English-only by default (see config.toml [embedding]). Measured
+# 2026-09-08: the same story in Spanish and English scored 0.758 and 0.600
+# cosine against a random-pair p99 of 0.634, so one of two translation pairs
+# was indistinguishable from an unrelated article. Italy and Mexico are
+# therefore covered by English-language sources.
 # Conflict outside categories A-D notifies only on a major development -- a new
 # offensive, a ceasefire, mass casualties, a state entering. Routine front-line
 # reporting goes to the digest.
 conflict_general_requires_importance = true
 
-# =========================================================== scoring =========
-# Fitted 2026-09-08 against 3,885 items and 40 real feedback labels.
-# See profile/CALIBRATION.md.
-
-[scoring]
-normalize = "zscore-per-block"
-veto_absolute = 0.60
-veto_margin_over_interest = 0.3