Display group hashes and identify groups from a description (LMFDB#5556)

Part (a): surface the isomorphism-invariant hash in the finite groups
interface. Abstract group homepages show the stored hash (with a search
link) whenever it is informative, i.e. hash is present and differs from
the label counter; add an optional, off-by-default "Hash" search column;
and linkify the two hash TODO popups in group_data. Subgroup pages get
nothing (subgroup_hash/quotient_hash are entirely NULL in the DB).

Part (b): new /Groups/Abstract/identify endpoint plus a form on the index
page and jump-box wiring for permutation input. The server computes the
LMFDB (Magma) hash in-process via libgap -- a faithful port of Hash.m in
new file identify.py -- with strict, no-eval parsers for permutation
generators, PC codes and matrices, a 10^6 order cap, and cysignals
alarm() timeouts. Lookup goes IdGroup (proof) -> gps_smallhash (complete
tables) -> (order, hash) on gps_groups, with mathematically honest
messaging (a hash match is not an isomorphism proof).

Verified: libgap hash port reproduces every stored value tested (512.11,
1536.947, 2016.i, 6561.4, 5120.cs, 1024.a, M11, Sp(4,3), abelian cases);
identify redirects/lists/errors and the alarm timeout+recovery exercised
via the Flask test client; new pytest cases and the full
test_abstract_groups.py (12) and test_browse_page.py (71) pass; pyflakes
clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: roed314