feat(ecosystem): compliant Praxis/Hexis integration + vendored build

Bring the Nexus/Praxis/Hexis integration in line with
MAVEN_ECOSYSTEM_ARCHITECTURE.md:

- Praxis over HTTP: drop the in-process praxis.db open (praxisstore/
  praxistools) and call praxisd's /api/v1/tools/* API via a new praxisClient.
  Honors the "no component reads another's DB" invariant (AC#12).
  PraxisConfig.DBPath -> URL.
- Hexis confirmation gate: mutating capabilities (ReadOnly=false) now park a
  bound pendingHexis confirmation and require a spoken "да" before executing;
  read-only run immediately (AC#7, no auto attention->action).
- Capability safety: >1 verb match is ambiguous -> ask instead of firing the
  first; ambiguous Nexus resolution asks for clarification (AC#2).
- Correlation IDs on Hexis execute, recorded in the cross-service trace.
- Bug: importance arrives as JSON float64 over HTTP, not int.
- Tests: confirm-gate, decline, read-only, and ambiguity paths.

Build: vendor/ bakes in the hexis client (replace-directed at a sibling repo
outside the Docker context); Dockerfile builds from vendor and no longer
`go mod download`s the unreachable replace paths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vendor/modernc.org/sqlite/AUTHORS

@@ -0,0 +1,34 @@
+# This file lists authors for copyright purposes.  This file is distinct from
+# the CONTRIBUTORS files.  See the latter for an explanation.
+#
+# Names should be added to this file as:
+#     Name or Organization <email address>
+#
+# The email address is not required for organizations.
+#
+# Please keep the list sorted.
+
+Angus Dippenaar <angusdippenaar@gmail.com>
+Artyom Pervukhin <github@artyom.dev>
+Dan Kortschak <dan@kortschak.io>
+Dan Peterson <danp@danp.net>
+David Walton <david@davidwalton.com>
+Davsk Ltd Co <skinner.david@gmail.com>
+FerretDB Inc.
+Harald Albrecht <thediveo@gmx.eu>
+Ian Chechin <ian00chechin@gmail.com>
+Jaap Aarts <jaap.aarts1@gmail.com>
+Jan Mercl <0xjnml@gmail.com>
+Josh Bleecher Snyder <josharian@gmail.com>
+Josh Klein <josh.klein@outlook.com>
+Logan Snow <logansnow@protonmail.com>
+Michael Hoffmann <mhoffm@posteo.de>
+Michael Rykov <mrykov@gmail.com>
+Morgan Bazalgette <morgan@howl.moe>
+Ross Light <ross@zombiezen.com>
+SUSE LLC <moio@suse.com>
+Saed SayedAhmed <saadmtsa@gmail.com>
+Steffen Butzer <steffen(dot)butzer@outlook.com>
+Toni Spets <toni.spets@beeper.com>
+W. Michael Petullo <mike@flyn.org>
+Zhenghao Zhang zhangzhenghao@hotmail.com