feat(ru): drop abbreviations from the Russian noun list

The list leaked abbreviations two ways: an OpenCorpora noun tagged Abbr without
Fixd (the declinable acronym ОГВЗ) slipped past the Abbr+Fixd seed filter, and the
РАН «(сокр.)» words (вуз, нэп, колхоз, гост, …) were kept on purpose by the old
policy.

Drop every abbreviation instead. A final pass in ru_stage2.py removes a word when
the orthographic note marks it «(сокр.)» (is_abbrev_note) or when every OpenCorpora
noun reading carries Abbr (oc_abbr_only — also the declinable огвз/заз the seed
filter missed). Homographs with a plain-noun reading survive (ваза «ВАЗ», рис).
Lexicalised words are rescued via manual_confirm.txt (колхоз, совхоз, рация,
спецназ, эсминец, дзот, дот, прораб, токамак, тэн, … and под — a real noun OC knows
only as ПОД); the bound prefix гос is vetoed in manual_reject.txt.

108 words removed from ru_scrabble / ru_erudit; en_sowpods unchanged. tools/README
documents the policy and that libmorph is required for a faithful rebuild.

tools/ru_stage2.py

@@ -170,6 +170,38 @@ def oc_function_word(word):
     return False
 
 
+def oc_abbr_only(word):
+    """True when every common-noun reading OpenCorpora gives word is an abbreviation (carries
+    the Abbr grammeme on its paradigm). Generalises oc_abbr_fixd_only past the Fixd
+    (indeclinable) requirement, so it also catches a *declinable* acronym that OpenCorpora
+    inflects through a full Abbr case paradigm without Fixd — огвз, заз — as well as the
+    indeclinable роно, тв, фио. A word with any non-Abbr noun reading (the homographs ваза
+    «ВАЗ», рис «РИС», под «ПОД»/под печи) is not abbreviation-only and is left alone."""
+    parses = D.get_word_parses(word)
+    if not parses:
+        return False
+    gp, pt = D.get_paradigm, D.parse_tag_string
+    has_noun = has_plain = False
+    for pid, idx in parses:
+        suf, tag, pre = gp(pid, idx)
+        pos, gr = pt(tag)
+        if pos != "NOUN":
+            continue
+        _, tag0, _ = gp(pid, 0)
+        _, gr0 = pt(tag0)
+        if PROPER & gr or PROPER & gr0:
+            continue
+        has_noun = True
+        if "Abbr" not in gr0:
+            has_plain = True
+    return has_noun and not has_plain
+
+
+def is_abbrev_note(note):
+    """True when the orthographic note marks an abbreviation («сокр.», e.g. вуз, нэп, колхоз)."""
+    return bool(note) and "сокр" in note
+
+
 def libmorph_analyze(words):
     """Map each word to (known, noun_lemma, codes) per libmorph; noun_lemma is None when it
     is not a common noun there. Empty result if the helper binary is not built."""
@@ -353,6 +385,20 @@ def build():
                     fate[y] = f"scrabble: вариант от «{x}» (через «и»)"
                     changed = True
 
+    # Abbreviations are not Scrabble words. Two independent signals catch them: the orthographic
+    # note marks «(сокр.: …)» (вуз, нэп, колхоз, гост, …); and OpenCorpora tags acronyms Abbr —
+    # both the indeclinable (роно, тв, фио) and the declinable ones the Abbr+Fixd seed filter
+    # misses (огвз, заз, гулаг). Drop every such word, except the lexicalised ones the maintainer
+    # rescues in manual_confirm.txt (колхоз, совхоз, рация, спецназ, … and под — a real noun
+    # OpenCorpora knows only as the abbreviation ПОД). The homographs that are real words with a
+    # mere abbreviation reading (ваза, рис) survive — oc_abbr_only requires *all* noun readings
+    # to be Abbr. Subtracted before the manual-reject veto.
+    confirm = {w for w in load(os.path.join(OUT_DIR, "manual_confirm.txt")) if cyr_ok(w)}
+    abbrev = {w for w in scrabble if w not in confirm and (is_abbrev_note(hmap.get(w)) or oc_abbr_only(w))}
+    scrabble -= abbrev
+    for w in abbrev:
+        fate[w] = "отброшено: аббревиатура (помета «сокр.» орфословаря или только Abbr-чтения в OpenCorpora)"
+
     # Manual rejections: words the maintainer vetoed — substantivized-adjective false nouns
     # a dictionary misreads as nouns (нёбный, акцизный, …). Subtracted last, so it overrides
     # every admission path above (OC seed / libmorph / note / manual_confirm / variant).